By Monica Agar, MD, Obstetrician and Gynecologist—Virtua OB/GYN

We're fortunate to live in a time when technology and research enables women to be healthier and more informed throughout their pregnancies. But, with knowledge, sometimes comes worry.

One worrisome thing many pregnant women experience is spotting (light bleeding). It’s very common, but it’s still scary when it happens.

Here are some reasons why spotting can occur throughout pregnancy. If you experience it, call your ob/gyn immediately to see what’s causing it and to ease your fears.

First trimester

First trimester bleeding can occur in up to 20 percent of pregnancies. Here are a few of the reasons why you may experience it.

Implantation spotting occurs when a fertilized egg implants in the uterine wall. This type of spotting can be heavy enough to be mistaken for a light period. It usually occurs 1-2 weeks after fertilization.

Sub-chorionic bleeding occurs when blood collects between the amniotic sac and the uterus. This can be accompanied by light cramping and can occur any time in the first trimester. Often, the blood is re-absorbed by the body.

Miscarriage can cause spotting or bleeding, as well as cramping and low back pain. Most miscarriages occur during the first 10 weeks. However, after the heartbeat is heard, miscarriage risks drop significantly.

Ectopic pregnancy happens when fertilization occurs outside of the uterus and the egg implants in the walls of the fallopian tubes; in rare cases, it can implant in the cervix or ovary. An ectopic pregnancy is a life-threatening condition that needs emergency treatment.

Molar pregnancy, though uncommon, occurs when a fertilized egg doesn’t develop into a fetus and becomes an abnormal growth instead.

Cervical trauma or changes can cause bleeding. This can happen following intercourse or gynecological exams.

Inflammation can cause bleeding and may be the result of infection—either sexually transmitted or non-sexually transmitted. This can happen during the second and third trimesters as well.

Cervical polyps and cervical cancer also can cause bleeding, but they’re the least likely reason.

Second/Third trimester

Later in pregnancy, the fetus is more developed and bleeding causes are quite different.

Placenta problems have a few causes, but all placenta problems result in immediate delivery by cesarean section.

• Placenta previa is a condition in which the placenta completely or partially covers the cervix. The placenta also can lay low in the uterus close to the cervix. With placenta previa, the placenta can become exposed during labor, which is a danger to the fetus. Sometimes, even basic activity like exercise or intercourse can cause bleeding. The placenta can move position as the pregnancy advances, so placenta previa can resolve during pregnancy. If it doesn’t, the woman would need to be delivered by cesarean section.
• Placenta abruption occurs when the placenta detaches or separates from the uterus. It can occur as a partial detachment or a complete detachment. A complete detachment is an emergent situation that threatens the pregnancy.
• Vasa previa is relatively uncommon, but occurs when fetal blood vessels, such as those from the placenta or umbilical cord, present over the cervix.

Preterm labor is when the cervix starts dilating before 37 weeks. In this circumstance, your doctor often will try to stop labor until you reach full term.

Bloody show is a type of bleeding women in labor often experience. It usually has a mucous-like consistency and can range in color from red to brown.  

Finally, it’s possible that the spotting you see is not related to your pregnancy at all. If you have hemorrhoids (which are common in pregnant women) or a urinary tract infection, you may see blood that’s a result one of those conditions.

It’s important to keep an eye out for unusual discharge or blood. If you’re ever concerned, your OB/GYN is the best resource to help you understand what’s going on and to make sure you and your baby are in the best of health.