Women who become pregnant within three months of stopping oral contraception (OAC) have a slightly increased risk of preeclampsia and premature birth of the child. This is the conclusion of Dutch research, published in the International Journal of Epidemiology.
‘The absolute risks are small, but the seriousness of the complications of preeclampsia and preterm birth are high,’ said epidemiologist Marleen van Gelder of Radboud university medical center, principal investigator of the study. ‘We saw an absolute risk of 3.5 percent for preeclampsia and 5.8 percent for preterm birth in women who became pregnant within three months of stopping OAC. In the control group, the group of women who had not used an oral contraceptive in the year before pregnancy, 1.8 percent developed preeclampsia and the risk of preterm birth was 3.6 percent.’ The researchers could not determine whether it made any difference what type of OAC someone used. ‘We cannot conclude whether the risk of quitting is related to which generation of OAC someone has used. The research population was too small for that,’ says Van Gelder.
Van Gelder indicates that it is not ‘100 percent certain’ whether there really is a causal relationship between the complications and the use of a COC. ‘On the other hand, we adjusted for most of the confounders, including smoking, age, education level and migration background. So there is a good chance that this can be explained causally.’ Van Gelder emphasizes that it is not yet known how the increased risk can be fundamentally explained.
The researchers found several more associations. For example, the risk of pre-eclampsia appeared to be increased when the woman had used a COC with a high dose of estrogen (≥ 30 micrograms) or a first or second generation COC. In contrast, there was a higher relative risk of preterm birth in women who used a COC with a low estrogen dose or a third generation COC. Van Gelder: ‘These findings were not unequivocal, so we cannot give clear advice to women who want to become pregnant.’
This study used the long-term cohort in the Pregnancy and Infant DEvelopment Study (Pride), led by Radboudumc. Of the 9054 women who participated in this study between 2012 and 2019, 6470 met the inclusion criteria. The women completed a digital questionnaire at weeks 10, 17 and 34 of the pregnancy and two and six months after the due date, followed by six-monthly questionnaires during childhood. The difference with previous studies on the influence of the timing of stopping OAC is that this study asked the women themselves when they stopped. Van Gelder: ‘This is more reliable than requesting data from the pharmacy, because women often decide for themselves when to stop taking OAC, even if not all strips have been used yet.’ The outcome measures of gestational diabetes, gestational hypertension, preeclampsia at ≥ 34 weeks gestation, preterm birth (< 37 weeks), low birth weight (< 2500 grams) and dysmaturity were also assessed via the questionnaire.
An important question is what general practitioners and other doctors should now advise to women who want to become pregnant who use or have used OAC. ‘It is not the case that this should lead to great unrest, but this study does contribute to a more complete picture of the possible disadvantages of using the contraceptive pill,’ says Van Gelder. In the press release from Radboudumc, co-author gynecologist Marc Spaanderman says: ‘Women can consider another form of contraception in the three months after stopping the pill. But that also has disadvantages, such as getting pregnant earlier and more menstrual complaints. In the end it remains a personal decision.’