While birth control pills are highly effective at preventing pregnancy, conception can occur even when taking them. Recognizing potential signs of pregnancy is important for individuals using oral contraceptives.
Understanding How Pregnancy Can Occur While on the Pill
Birth control pills work by releasing hormones, typically estrogen and progestin, to prevent ovulation, thicken cervical mucus, and thin the uterine lining to deter implantation. Despite their high effectiveness of over 99% with perfect use, “typical use” effectiveness is closer to 91-93%, meaning around 7 out of 100 pill users may become pregnant each year. This discrepancy often arises from inconsistent pill-taking habits, such as missing doses or taking pills at different times daily.
Additional factors can reduce the pill’s effectiveness. Severe vomiting or diarrhea lasting more than 48 hours can prevent the body from absorbing the hormones adequately. Certain medications, including some antibiotics, anticonvulsants, and the herbal supplement St. John’s Wort, can interfere with how the pill works. In rare instances, inherent pill failure can occur.
Common Symptoms of Early Pregnancy
Signs and symptoms can indicate early pregnancy. A missed period is often the first noticeable sign, even if your expected withdrawal bleed does not occur. Nausea, capable of occurring at any time of day, is a frequent symptom, typically starting between 4 to 6 weeks of pregnancy.
Breast tenderness or swelling can also signal early pregnancy. Increased fatigue occurs due to elevated progesterone levels. Other signs include more frequent urination, light spotting (implantation bleeding), and changes in appetite, such as food cravings or aversions. Headaches, dizziness, and mood swings are also common in early pregnancy due to hormonal shifts.
Distinguishing Pregnancy Symptoms from Pill Side Effects
Differentiating early pregnancy symptoms from the side effects of birth control pills is challenging, as many overlap. Both pregnancy and the pill can cause nausea, breast tenderness, fatigue, headaches, and mood changes. Birth control pills can induce nausea, and taking the pill on an empty stomach might exacerbate this. Breast tenderness is a common side effect when starting birth control pills or due to hormonal fluctuations from the pill.
Irregular bleeding or spotting is another symptom that can lead to confusion. While implantation bleeding in early pregnancy is usually light and lasts a day or two, birth control pills can also cause breakthrough bleeding or even lead to missed withdrawal bleeds, mimicking a missed period. A new onset of multiple, distinct symptoms, or a change in the severity of existing symptoms, might suggest pregnancy rather than typical pill side effects. If you have missed two or more pills and experience heightened fatigue, this is a stronger indicator of pregnancy.
Steps to Confirm a Suspected Pregnancy
If you suspect pregnancy while on the pill, taking a home pregnancy test is the initial step. These tests detect human chorionic gonadotropin (hCG), a hormone produced after implantation, and their accuracy is not affected by birth control hormones. For the most reliable result, take the test about a week after a suspected missed period or after noticing concerning symptoms.
Using the first morning urine provides the highest concentration of hCG, increasing test accuracy. If the home test is positive, or if you receive a negative result but still experience pregnancy symptoms, follow up with a healthcare provider for confirmation. A doctor can perform a blood test, which can detect pregnancy earlier than urine tests, or an ultrasound for definitive confirmation.
What to Do If You’re Pregnant
Upon receiving a positive pregnancy test result, stop taking your birth control pill. Contact a healthcare provider without delay to confirm the pregnancy and discuss prenatal care options. While taking birth control pills in early pregnancy is not linked to increased birth defects, there is an elevated risk of ectopic pregnancy, particularly with progestin-only pills.
Your doctor will provide guidance on lifestyle adjustments, such as avoiding alcohol, smoking, and certain medications that could be harmful during pregnancy. Discuss all options and next steps with your healthcare provider to ensure the best possible care.