A matched group of women who conceived during a 2-month period in 1971 was used to trace some parameters involved in their decision to carry their pregnancies to term or to seek an abortion.

Several specific indices to the decision were considered: whether coitus was anticipated; whether the pregnancy was planned; whether birth control methods were used; and how the pregnancy ended. The effects of age, marital status, religion, reasons for the abortion or carrying the pregnancy to term, and attitude towards a possible delivery were also studied.

It was found that coitus was anticipated by the majority of women, but pregnancy was unplanned for. Two-thirds of the women who did not want to become pregnant were not using a contraceptive method yet, regardless of whether birth control was used or not, one of three women chose to have an abortion.

Among the most common reasons for women indicating that contraceptive measures were not used were: “I didn’t want sex to seem planned” and “I thought I was in a safe period”. The decision to have an abortion usually depended upon the woman’s marital status, age, religion, and previous use of birth control. Surprisingly, among women who had not planned to become pregnant, the percentage of women choosing abortion was the same from both subgroups of women who used or did not use contraception. It was also surprising that no strong relationship seemed to exist between the type of contraceptive technique used and the decision to have an abortion.

Women who planned ahead to have an abortion if they became pregnant were more often using contraception;thus for these women abortion was not a primary method of family planning but a back-up for failed contraception. Women who had their babies, infrequently considered abortion as an alternative.

It was predicted and found true that women who positively viewed the prospect of having a child chose to carry the pregnancy to term while those who expressed unhappiness at having a baby chose abortion. Unexpectedly, we found the overwhelming majority of women who claimed “I would be neither happy nor unhappy to have this baby” chose to have an abortion. Thus a woman’s so-called neutral statement regarding a desire was generally seen not to be neutral.

Our use of a pregnant population of women who conceived at the same time (conception cohort) for the analysis of the decision of whether to have an abortion or carry to term, when abortion is legal, thus seemed to be feasible and practical.


The Hawaii Pregnancy, Birth Control and Abortion Study is a state-wide investigation conducted continuously since March 1970, the date of the passage of the law which legalized abortion in Hawaii, essentially allowing abortion on request. Our group studies abortions and live births in the state using the pregnant population that presents itself to hospitals throughout the state (all legal abortions must be done in hospitals). From every hospital performing abortions in Hawaii. we collect data from hospital charts and from self-administered questionnaires given to the women. These data provide information not only on the woman’s reproductive history, but also on her attitudes and practices in regard to sexual behaviour, birth control usage, and reasons for carrying the pregnancy to term or having an abortion. The present study will report on some behavioural and contraceptive correlates of women from a special population pool which we refer to as a conception cohort.

Cohort construction

The conception cohort consists of: (a) women who gave birth during a given period of time (April and May 1971), and (b) women who had abortions but whose pregnancies otherwise would have come to term during April and May 1971. The abortion patients were selected on the basis of the calendar month during which they had their abortions, and the estimated gestation at abortion (in 4-week intervals). Because both criteria were coded in rather broad categories, each case was then weighted on the basis of the probability that the birth actually would have occurred during the target maternity period. We call this a “conception cohort”, because theoretically it includes all women who conceived at the same time, and therefore were making the decision to have the baby or have an abortion, at the same time. Excluded from consideration was any woman who had a stillbirth, spontaneous abortion or illegal abortion. We are reporting here on only the first of six planned cohorts covering 3 years of data; with additional data, some results may be different.

Text-fig. 1. Hawaii pregnancy, birth control and abortion study,
April-May 1971 cohorts. Numbers represent weeks gestation at abortion.

Demographic data were available on every maternity and abortion patient in the state who met the criteria for inclusion in the cohort. Questionnaires were obtained from about 45% of the women who had live births and 56% of the women obtaining abortions in the state during the period of the cohort. The questionnaire samples in the cohort were weighted on the basis of the 100% demographic data available to correct for small response biases. Thus the final questionnaire sample of 1579 cases fairly accurately represents the composition and relative proportions of the corresponding conception cohort for the State of Hawaii. The sample is about half the size of the actual population of women involved.

Decision making

Using this cohort population, we have attempted to trace several parameters involved in the women’s pregnancies. For this report, we emphasize coital and contraceptive factors involved in becoming pregnant and the relationships of several of these factors to the decision to maintain the pregnancy to term or to have an abortion.

While these are indeed complex and inter-relating variables, they are dealt with here as independent variables but mention is made of other related factors which we have found to intervene.

It might be hypothesized that decisions related to coitus, birth control and pregnancy outcomes are related. For example, a woman may obviously plan to have, and actually have, intercourse while refraining from using contraceptives in order to have a desired baby. On the other hand, it has been well documented that many women who have coitus regularly without using a birth control method do not want to become pregnant or have children. Table 1 indicates how some of these factors may be considered.

Table 1. Sexual behaviour and reproduction:
a decision making process

Coitus Birth control Pregnancy
Planning and attitudes
How considered Planning
Outcome and practices
Choice of method
Use of method


From our cohort sample, we first can ascertain whether coitus was an expected event. It is apparent that a woman who desires to become pregnant expects to have coitus but this is not apparent of women who did not plan to become pregnant. Relative to the pregnancy under discussion, coitus was reported as unexpected by 6% (96) of the women. This can be interpreted that coitus was expected in 94% (1483) of the cohort population (Text-fig. 2).

Text-fig. 2. Coitus–planning–pregnancy–birth control use–pregnancy outcome.

Pregnancy planning

Among those women who had an expected coitus, 45% planned to become pregnant.  We ascertain if a pregnancy was planned by two methods in concert.  The first involves a “Yes” or “No” response to the question, “Were you using any birth control technique when you became pregnant?”, followed by the woman selecting, from a series of multiple choices, “I wanted to be pregnant” for her reason. The second, used for women who go on to deliver, is a selection of “My husband and I planned to have this child” as one of many possible reasons for maternity. Both correlate well. This 45% represents 42% of the total pregnant cohort population. Thus, put another way, the pregnancies of 58% of the cohort population were unplanned.

Surprisingly, in our cohort population we found many unmarried girls who claimed they became pregnant by choice. About 7-10% of the women who indicated they were single or going steady said they wanted to become pregnant; 27-29% of women who were living with a man or engaged reported similarly. Among married women, 63 indicated they were pregnant by choice (Table 2).

Table 2. Planned pregnancy within marital status among those not using a contraceptive technique*

Marital status at conception
No. of pregnant women No. of planned pregnancies % of planned pregnancies
Never married
   Living together
954 604 63.0
 34   1  2.9

* Weighted figures.

Use of birth control

When a pregnancy is planned, it would be anticipated that coitus would occur without contraceptive measures, and all planned pregnancies would be carried to term. Vice versa, it would be expected that when babies are not desired. some contraceptive methods would be utilized and if pregnancy were to cur, when abortion is legal, it would be the solution to the dilemma. The former hypothesis was generally substantiated, the latter hypothesis rarely so.

As expected, our data indicate that almost all women who planned to become pregnant (97%) did not employ any contraceptive methods. Surprisingly, 3% of the women who wanted to become pregnant nevertheless reported using a contraceptive technique (Text-fig. 2). It is quite possible that these 3% were using rhythm or other methods in order to achieve pregnancy. Among the women who wanted to become pregnant, 26.4% indicated that they had been trying to conceive for more than 1 year; 3.5% of these for more than 3 years; and another 3.5% for more than 5 years.

The majority of sexually active women who did not plan to become pregnant did not use a contraceptive method. Many reasons exist for not using a contraceptive technique to prevent an unwanted pregnancy. With an unexpected coitus, as reported by 6% (96)of the women in the cohort, a report of “no method used” would seem acceptable (despite the fact that withdrawal might have been advocated). There nevertheless remained 57% (520) of all those women not planning to become pregnant who expected coitus, yet did not use any form of contraception.

In addition to considering the coitus unexpected, the reasons given for not using birth control methods vary with several factors such as age and marital status. Young and single women tended to indicate: “I didn’t want sex to seem planned”. Married as well as single women reported: “I thought I was in a safe period”.

‘It’s against my religion to use birth control” and “The father wouldn’t let me use birth control” were reported with about equal frequency and account for 123 of the 520 women who, despite the fact that they anticipated coitus and did not want to become pregnant, were not using a birth control method; 72% of these non-contracepting women giving either or both of these last two reasons were Catholic (88 of 123).

A large percentage (33%) of the pregnant women who did not plan to become pregnant used contraceptive methods, yet became pregnant. This is about 19% of the total cohort population. It must be recalled that all these data are derived from a pregnant population. Those women who are effective contraceptors, probably the majority of sexually active women, do not enter our sample. Using 1970 census data, the number of women of reproductive age in Hawaii was approximately 194,000. Since there were about 19,500 women (10% of the possible population) pregnant during 1971 (in round figures a combined total of 15,900 live births and 3600 abortions), we can extrapolate and say that, theoretically, 19% of these, roughly 3800 or 1-2% of the state’s population of women of reproductive age, became pregnant due to birth control failure that year.

Among these contraceptive failures, all methods were represented. The pill was used by 31% of all those using birth control at conception who did not plan to become pregnant. Foam users represent the next largest group, 22% of this contraception population. The rhythm method was reportedly used by 18%. Regrettably, we do not know what proportions of the total state population of women using contraception were using the various techniques so it is not possible to calculate contraceptive efficiency from these data.

There was a surprising reversal of contraceptive usage among religious groups (Table 3). Comparing Catholics with Protestants and Buddhists, the other two large religious groups in the state, we find proportionately fewer Catholics having used rhythm and more having used the pill.

Table 3. Religion and use of birth control*

No. of women using: Total using BC
Rhythm Pill IUD Other
 6 (21%)  7 (25%)  0  (0%) 14 (50%)  27
14(13%) 47 (44%)  7  (7%) 38 (36%) 106
24 (18%) 39 (30%) 17 (13%) 50 (39%) 130
 6 (15%)  7 (18%) 10 (25%) 17 (42%)  40
 3 (20%)  3 (20%)  2 (13%) 7 (47%)  15

* Weighted figures.

Recalling again that it is only the failures that we are seeing in our population, this may reflect that Catholics use rhythm best and pills poorest. Of course, our findings could also mean that some of the classical associations of religion with contraceptive method might need re-examination.

Particularly peculiar was our finding that among the group of contracepting women, four women were found who supposedly had had their tubes tied, yet became pregnant. Investigation of the medical records confirmed that two of these women had had the procedure indicated; the records were incomplete for the other two. One of these four women has now had a hysterectomy.

The use of birth control methods in general increased with the strength and type of the sexual relationship (Table 4). In general, in the cohort population engaged couples used birth control measures with about the same frequency as did couples going steady (19.1% and 17.9%). Married couples and couples living together also used birth control measures in about the same proportions (40.2% and 38.2%), Regrettably, single “unattached” girls, i.e. those with the least firm relationships and thus least ready for family unions, used birth control least (13.6%).

Table 4. Use of birth control within marital status for unplanned pregnancies

Marital status at conception
No. of pregnant women No. of women using BC % women using BC
Never married
281 54 19.2
 88 12 13.6
112 20 17.9
   Living together
 34 13 38.2
 47   9 19.1
595 239 40.2
 41   8 19.5
916* 300*  

* Weighted figures.

Pregnancy outcome

We can now examine how women having become pregnant, whether planned or unplanned, having used contraceptive methods or not, terminated their pregnancies when abortion was a legal choice (Text-fig. 2).

With planned pregnancies, it is to be expected that the women will go to term and deliver. This was indeed demonstrated in the vast majority (98%) of the cases. Significantly, 2% of the women who had originally planned to have a baby and did not use birth control, after becoming pregnant chose to have an abortion. Some of these women reported that they had been trying for some time to become pregnant but now were choosing an abortion for various reasons such as: “I am still single”, “I am not able to cope with a child at this time”, “The child is not my husband’s”, “My marriage is too shaky”, “My husband doesn’t want the child”, and “A child would interfere with my or the father’s job or education”. The mean age for these women was 23.1, and the median age was 24, so age generally did not seem to be a factor.

Surprisingly, among those women who had not planned to become pregnant, the percentage of women choosing an abortion is the same from both subgroups of women who used or did not use contraceptive methods; 31% and 32% respectively (Text-fig. 2). Thus the use of birth control per se did not seem to be predictive of resolve not to have a baby.

It is also surprising that there is no strong correlation between the type of contraceptive technique used and the decision to have an abortion. It had been hypothesized that a woman using a “good” contraceptive such as the pill would be more likely to be determined not to have a child than is a woman who was relying on rhythm or withdrawal. In fact the findings seem to indicate the opposite (Table 5).

Table 5. Contraceptive use* and choice of abortion related to marital status at conception

Contraceptive method used
Total no. using this method Total no. (%) choosing abortion No. never married using this method No. (%) never married choosing abortion No. married using this method No. (%) married choosing abortion
21 (32%)
 6 (33%)
21 (46%)
20 (38%)
11 (38%)
14 (39%)
14 (14%)
  5 (31%)
7 (58%)
7 (70%)
11 (73%)
9 (69%)
2 (33%)
7 (53%)
3 (60%)
14 (26%)
 5 (29%)
14 (39%)
 9 (24%)
 1  (6%)
10 (33%)
 5  (6%)
 1 (10%)

* Some couples use combined methods.

The data indicate that of all women who were using oral contraceptives when they became pregnant, only 14% chose to have an abortion. If the women were married and became pregnant while using the pill, only 6% chose abortion. An incidence of abortion from between 30% and 40% of women was associated with the other routinely used contraceptive methods, except the condom and the IUD. This was generally reduced markedly if the woman was married, and increased markedly if the woman was single.

If the condom was used, a higher proportion of women in each marital status group chose abortion. Use of this contraceptive technique might thus be considered to reflect a greater resolve not to have a baby. If the IUD was used, independent of marital status, about one in three women chose abortion.

All four of the women who supposedly had had tubal ligations but became pregnant chose to carry their pregnancy to term. Two considered it as “natural or God’s will” and two claimed they did not believe in abortion.

For those women choosing to have an abortion, the decision to do so was made as soon as the woman knew she was pregnant in 63.0% of the cases; before the pregnancy in 85%, and just before the abortion (“recently”) in 23.9% of the cases. Those women who planned ahead to have an abortion if they became pregnant were more often using contraceptives. For this group, therefore, it does not seem as if abortion was a substitute contraceptive method; rather, it was a back-up for failed contraception. No clear relation exists between contraceptive use and when the decision to have an abortion was made in the other groups.

For women going on to have their babies, relatively few considered abortion as an alternative. Among those women who did not use contraceptive techniques, 91.1% indicated they did not consider having an abortion; among those women who did use contraceptives, 86.4% indicated they did not consider having an abortion.

As reported previously by Smith et al. (1971) and Steinhoff, Smith & Diamond (1972), the reasons most often given by a woman for deciding to have an abortion were: “I am not married”, “I cannot afford the child financially”, “I already have enough children”, “A child would interfere with my education”, and “I am not able to cope with a child at this time”.

The reasons vary with contraceptive usage and this is related to age and marital status. For example, older or married women were more likely to have been using contraceptive techniques and indicated they chose abortion because they could not cope with a child or considered they had enough children already.

The most frequently given reasons for carrying the pregnancy to term were, as might be expected, related to whether the baby was planned and whether contraceptive techniques were used.

Quite often when the woman found she had an unplanned pregnancy, she and her husband decided to have the child anyway. Disapproval of abortion was given as a reason for having the baby by about 13% of the women with unplanned pregnancies who had not used contraception. Similarly, of women who had used contraception, 10% said they did not approve of abortion so were having the baby.

The decision of a pregnant woman to have an abortion or carry to term is often thought to be related to marital status, age and religion. We have considered these factors along with contraceptive use (Text-fig. 3).

Text-fig. 3. Choice of abortion related to
marital status at conception and birth control use.

Marital status was seen to relate with contraceptive use to predict the decision regarding pregnancy termination. Non-married contraceptors were more likely to have an abortion than were married contraceptors; non-married women, in general, were more likely to have an abortion than were married women. This is in sharp contrast to national findings under illegal conditions in the late 1950s (Gebhard et al., 1958) but is in keeping with recent findings in New York and California (Berkov & Sklar, 1972; Duffy, 1971; Pakter & Nelson, 1971; Russell, 1969; Tietze & Lewit, 1972). It must nevertheless be emphasized that a large percentage of women, regardless of their marital status, chose to carry the pregnancy to term (Text-fig. 3).

This relationship of marriage to choice of abortion was, as might be expected, related to age. The older married woman more often chose an abortion than did the younger. While in absolute numbers more women under 25 years had abortions, a much greater proportion of pregnant women 25 years and older chose abortion than did younger women (Text-fig. 4).

Text-fig. 4. Choice of abortion related to
marital status and age at conception.

Religion, too, was related to how a woman terminated her pregnancy. Regardless of marital status, Catholics consistently chose abortion less frequently than did Protestants or those women who professed no religion (Text-fig. 5). Buddhists, too, chose abortion less frequently than Protestants but this was due to a greater percentage of their pregnancies being planned.

Text-fig. 5. Choice of abortion related to
marital status at conception and religion.

With marital status, we have related a simple multiple choice question as to how each woman viewed the prospect of having a child and her choice of pregnancy outcome. Predictably, almost all women who expressed “I would be unhappy to have this baby” decided to have an abortion. Less predictable is the finding that a number of women chose abortion despite their saying “I would be happy to have this baby”. Least predictable was the finding that the overwhelming majority of women who claimed “I would be neither happy nor unhappy to have this baby” chose abortion. A woman’s so-called neutral statement regarding her desire to have a baby when she is pregnant was thus generally seen not to be neutral.

Finally, we correlated some early steps in the decision-making process with the final pregnancy outcome. Of those women not using contraceptives who claimed “Sex was unexpected”, 25% had their pregnancies terminated; so, too, did 26% of those women who claimed “I thought I was in a safe period”. These two groups of women who were non-contraceptors and who did not plan to become pregnant comprise 68% of those who chose abortion. Of those who indicated that their pregnancy was the result of a birth control failure, 31% chose abortion.

Text-fig. 6. View of baby related to marital status.


We have attempted to show, by using a fairly complete population of pregnant women (conception cohort), a decision-making process relating how sexual behaviour, birth control use and pregnancy outcome could be monitored under conditions where abortion is legal and access to the total population was possible. Starting with the expectancy component of coitus, we traced pregnancy planning, birth control use and pregnancy outcome. The analysis was basically sequential but it is obvious that the decision-making process cannot be fully considered as a linear progression of events. Coitus for the majority of women was anticipated and yet pregnancy was not generally planned for. Regrettably, two-thirds of the women who had not planned their pregnancies had not used a birth control method to prevent such consequences. Of these women, as of the one-third that did attempt to prevent conception, only one out of three women elected to have an abortion. Marital status, age and religion were seen to affect the decision as to whether or not to have an abortion, but we also found that a woman’s acceptance of her sexuality and attendant use of contraception related to these factors and correlated with how she decided to terminate her pregnancy.

This use of conception cohorts and the analysis of the decision-making process is believed to provide a model that is applicable elsewhere. Different independent variables may be used as filters at any stage to provide analyses of the decision-making process for any group under study. For example, one could monitor the change in dependent variables such as coitus or birth control usage, while using as independent variables religion, socio-economic status or age. Other models for similar analysis have been proposed (e.g. Friedman, 1972). The present model seems advantageous primarily because it provides a built-in comparative control group of women who planned their pregnancy and indeed chose to deliver. This type of analysis of choice deals with a selected population from among a larger one available to us (Diamond et al., 1972). We consider that this gives a better reflection of the actual parameters attendant on the decision to have an abortion or carry to term, particularly if used repeatedly so that controlled comparisons can be made over a period of time.


This work was supported mainly by the National Institutes of Health Grant NICHHD HD-05853 and in part by the Ford Foundation and the East-West Center Population Institute. We would also like to acknowledge the help of Mr Kay H. Hoke, Mrs Alice M. Beechert and Mr Mark Takaguchi.

This is Report No. 5 of the Hawaii Pregnancy, Birth Control and Abortion Study.



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