When you are using combined hormonal birth control pills, the regular, period-like bleeding you experience is known as a withdrawal bleed, not a true menstrual period. Understanding the difference is critical to knowing what to expect if you are on the pill and suspect a pregnancy.
The Physiology of a Withdrawal Bleed
In a natural menstrual cycle, ovulation occurs, and the uterine lining thickens to prepare for a fertilized egg. If the egg is not fertilized, hormone levels drop, and the lining is shed as a period.
Oral contraceptives work by suppressing ovulation and keeping hormone levels consistent. During the placebo or hormone-free week, the sudden drop in hormones triggers the uterine lining to shed, resulting in a withdrawal bleed. This bleed serves no medical purpose but historically offered reassurance that the user was not pregnant.
Why a Normal Withdrawal Bleed Will Not Occur During Pregnancy
If you become pregnant, your body produces the hormone human chorionic gonadotropin (hCG), which prevents the uterine lining from shedding, so a normal withdrawal bleed cannot occur. The pregnancy requires this lining to continue developing. Therefore, the absence of your expected withdrawal bleed during the placebo week is a primary sign that you may be pregnant and a reliable indicator to take a test.
Differentiating Pregnancy-Related Bleeding from Withdrawal Bleeds
Though you will not have a normal withdrawal bleed while pregnant, other types of bleeding can happen and be mistaken for one.
Implantation Bleeding
One of the most common causes of early pregnancy bleeding is implantation bleeding. This light spotting occurs when the fertilized egg burrows into the uterine lining. It can happen around the time your period would normally be due and is often mistaken for a very light, early period.
Other Sources of Bleeding During Early Pregnancy
- Cervical Changes: Increased blood flow to the cervix in early pregnancy can make it more sensitive, leading to spotting after sexual intercourse or a gynecological exam.
- Ectopic Pregnancy: In this dangerous condition, the fertilized egg implants outside the uterus, most commonly in a fallopian tube. Bleeding, often accompanied by severe abdominal pain, can occur.
- Miscarriage: Vaginal bleeding can be a sign of a threatened or completed miscarriage, especially when heavy and accompanied by cramping.
Comparing Bleeding Types
To help you distinguish between the different types of bleeding, consider the following characteristics:
| Characteristic | Withdrawal Bleed (On the Pill) | Implantation Bleeding (Early Pregnancy) | Breakthrough Bleeding (On the Pill) |
|---|---|---|---|
| Timing | During the placebo pill week, consistently scheduled. | Roughly 10-14 days after conception, around the time a period would start. | Any time outside of the placebo week, especially in the first few months or after a missed pill. |
| Color | Ranges from light to dark red, similar to a typical period. | Often pale pink, rust-colored, or brownish. | Varies; can be pinkish, reddish, or brownish. |
| Flow | Predictable, heavier flow similar to a period. | Very light spotting that does not typically fill a pad or tampon. | Usually light and inconsistent, often described as spotting. |
| Duration | Generally lasts 3-7 days, similar to a period. | Can last anywhere from a few hours to a couple of days. | Often lasts a few days, but can be a one-off event. |
When to Take a Pregnancy Test
Given the different types of bleeding that can occur, the most reliable way to confirm or rule out pregnancy is with a pregnancy test. Here's what you should know:
- Birth control does not affect the results: The hormones in birth control pills do not interfere with the detection of the hCG hormone that a pregnancy test looks for.
- Take a test if you miss a bleed: If you miss your expected withdrawal bleed while taking your pills correctly, you should take a pregnancy test.
- Take a test with unusual bleeding: If you experience spotting that seems different from your normal cycle, particularly if you missed any pills, a test is a good idea.
- Look for other symptoms: Other early pregnancy signs like nausea, breast tenderness, or fatigue could be confused with pill side effects. If these symptoms persist, take a test.
What to Do If You Suspect Pregnancy
If you have taken a pregnancy test and it is positive, or you have strong reason to believe you are pregnant, the following steps are recommended:
- Stop taking the birth control pill. While taking the pill early in pregnancy is generally not considered harmful, you should cease use as soon as you know you are pregnant.
- Contact your healthcare provider. They can confirm the pregnancy with a blood test or ultrasound, and provide further guidance on what to do next.
- Be aware of ectopic pregnancy risk. Although rare, there is a slightly increased risk of ectopic pregnancy if conception occurs on the pill. Any severe abdominal pain and bleeding should be considered an emergency.
- Consider your next steps. Your healthcare provider can discuss your options regarding the pregnancy and any related health concerns.
For more detailed information on contraceptive methods and safety, you can refer to authoritative sources like the CDC's resources on contraception.
Conclusion
In short, no, you do not still get a normal withdrawal bleed if pregnant on the pill. A typical withdrawal bleed is a reassuring sign that you are not pregnant, as the hormones of pregnancy prevent the uterine lining from shedding in that manner. However, early pregnancy can cause other forms of bleeding, like implantation spotting, which may be confusing. The most reliable course of action for a missed bleed or unusual spotting is to take a home pregnancy test. If the result is positive, contact your healthcare provider immediately for confirmation and next steps.
