Took Birth Control Before You Knew You Were Pregnant?

What does the evidence say about birth control pills during pregnancy?

1. A population-based drug-safety screening study found most oral contraceptive drugs among the medications not associated with an increased risk of major congenital malformations after first-trimester exposure, in the same no-increased-risk group as most proton-pump inhibitors and oral antihistamines. 1
2. A cohort study of over 6,400 pregnancies found that continuing oral contraceptives right around conception was associated with a modestly higher risk of preterm birth and low birthweight, with the risk strongest when the pill was stopped zero to three months before pregnancy began. 2
3. The same study found a possible link between periconceptional pill use and preeclampsia, though that specific result fell just short of standard statistical significance, and no significant link turned up for gestational diabetes or a baby measuring small for its gestational age. 2
4. A large Danish cohort study following 1.4 million children found a modest overall increase in childhood mortality among those exposed to hormonal contraception in early pregnancy, though the result for oral combined pills specifically was not statistically significant on its own, and the authors cautioned that the absolute numbers involved were small. 3
5. Combined oral contraceptive pills contain a combination of estrogen and a progestin and work primarily by suppressing ovulation, which is why continuing them without realizing you're already pregnant doesn't introduce a different drug mechanism than everyday contraceptive use, just an unintended pregnancy alongside it. 4

Is birth control pills safe in each trimester?

• First trimester. This is the window the concern is actually about. Once your test is positive, stop the pill and call your provider. Most studies haven't tied inadvertent exposure to a higher rate of birth defects, though newer data links continuing right around conception to a modestly higher chance of preterm birth and low birthweight.
• Second trimester. By now you've stopped and the pregnancy is progressing on its own hormonal course. There's no special monitoring protocol tied to early pill exposure alone, though it's worth confirming it's noted in your prenatal chart if it wasn't already covered at your first visit.
• Third trimester. Nothing about third-trimester care changes because of brief pill exposure before you knew you were pregnant. The relevant window was the first few weeks, and routine prenatal care from here covers what actually matters now.