A true menstrual period, which involves the shedding of the uterine lining after ovulation, does not happen once pregnancy is established. While some individuals may experience bleeding during pregnancy, this is not a typical menstrual period. This bleeding can have various causes, some benign and others requiring medical attention.
Why a True Period Doesn’t Occur During Pregnancy
The absence of a menstrual period during pregnancy is governed by hormonal changes. After conception, the body produces hormones that maintain the uterine lining and prevent its shedding. Progesterone levels remain elevated, signaling the uterus to retain its thickened lining to support the developing pregnancy.
Human chorionic gonadotropin (hCG), produced by the developing embryo, signals the ovaries to continue producing progesterone. This further ensures the uterine lining remains intact. This hormonal environment suppresses ovulation and the cyclical shedding of the endometrium, which are hallmarks of a menstrual period.
Common Causes of Bleeding in Early Pregnancy
Bleeding in the first trimester is common, affecting about 1 in 4 pregnant individuals, and does not always signify a serious problem. One frequent cause is implantation bleeding, which occurs when the fertilized egg attaches to the uterine wall. This occurs around 6 to 12 days after conception, often near the expected time of a menstrual period. Implantation bleeding is light spotting, appearing as pink or brown discharge, lasting for a few hours to a couple of days, and is not heavy enough to soak through a pad.
Changes to the cervix can also lead to light bleeding in early pregnancy. Increased blood flow to the cervix during pregnancy makes it more sensitive, and activities like sexual intercourse or a pelvic examination can sometimes trigger minor bleeding. While often harmless, any bleeding should be reported to a healthcare provider.
More serious causes of bleeding in early pregnancy include miscarriage and ectopic pregnancy. A miscarriage, the loss of a pregnancy before 20 weeks, involves vaginal bleeding that can range from light spotting to heavy flow with bright red blood or clots. This bleeding is accompanied by abdominal cramping or lower back pain, and sometimes the passage of fluid or tissue from the vagina.
An ectopic pregnancy, where the fertilized egg implants outside the uterus, most commonly in a fallopian tube, is a medical emergency. Symptoms include vaginal bleeding, accompanied by severe abdominal or pelvic pain, which may be sharp and localized to one side. Dizziness or fainting can also occur due to internal bleeding.
Understanding Bleeding in Later Pregnancy
Bleeding in the second or third trimester of pregnancy is more concerning and requires immediate medical evaluation. Conditions affecting the placenta are common causes for bleeding during this later stage. Placenta previa is a condition where the placenta partially or completely covers the cervix. Its main symptom is painless, bright red vaginal bleeding, which can occur intermittently.
Another condition is placental abruption, where the placenta separates from the inner wall of the uterus before birth. This results in painful, dark red vaginal bleeding, which may or may not be visible depending on whether the blood is trapped behind the placenta. Accompanying symptoms can include sudden and ongoing abdominal pain, uterine tenderness, and frequent contractions.
A rare cause of bleeding in later pregnancy is vasa previa, where fetal blood vessels within the membranes cross over or near the cervix. If these unprotected vessels rupture, often when the membranes break, it can lead to painless vaginal bleeding that is fetal blood, posing a significant risk to the baby. Preterm labor can also cause bleeding, accompanied by contractions and other signs of labor before 37 weeks of pregnancy.
When to Seek Medical Attention for Bleeding
Any vaginal bleeding during pregnancy should prompt a call to a healthcare provider for advice and support. While light spotting in early pregnancy may not always indicate a serious issue, it is important for a medical professional to assess the situation. Healthcare providers will inquire about the amount, color, and duration of the bleeding, as well as any accompanying symptoms.
Immediate medical attention is necessary if the bleeding is heavy, meaning it soaks through two pads per hour or involves passing blood clots the size of golf balls. Other warning signs that require urgent care include severe abdominal or pelvic pain, intense cramping, dizziness or fainting, fever, chills, or the passage of tissue from the vagina. These symptoms could indicate a serious complication, and prompt evaluation ensures the best possible outcome for both the pregnant individual and the baby.