7 pregnancy complications to watch out for

Most pregnancies are uncomplicated. That said, it's helpful to know which serious medical issues are most likely to affect expecting moms. Here's a quick guide to the seven most common pregnancy complications, listed from most frequent to least.

Your doctor or midwife will watch for these pregnancy complications – and others – throughout your pregnancy, using physical exams, lab tests, and ultrasounds to help diagnose any problems that arise. Meanwhile, you can help your caregiver by attending all your prenatal appointment and reporting any troubling symptoms.

Miscarriage

Miscarriage is the loss of a pregnancy in the first 20 weeks. About 15 to 20 percent of known pregnancies end in miscarriage, and more than 80 percent of miscarriages happen before 12 weeks. Most first-trimester miscarriages are believed to be random events caused by chromosomal abnormalities in the fertilized egg that keep the embryo from developing. Vaginal spotting or bleeding is usually the first sign, so call your healthcare practitioner right away if you notice it (although it's not uncommon to spot or bleed in early pregnancy even if you're not miscarrying). If your practitioner suspects a miscarriage, she'll order an ultrasound to see what's going on in your uterus and possibly do a blood test.

Premature labor and birth

If you start having regular contractions that cause your cervix to begin to open (dilate) or thin out (efface) before you reach 37 weeks of pregnancy, you're in preterm or premature labor. When a baby is delivered before 37 weeks, it's called a preterm birth and the baby is considered premature. About 12 percent of babies in the United States are born prematurely. Preterm birth can cause health problems or even be fatal for the baby if it happens too early. The more mature a child is at birth, the more likely he is to survive and be healthy.

Read more about the causes and chances of preterm labor.

Low amniotic fluid (oligohydramnios)

The amniotic sac fills with fluid that protects and supports your developing baby. When there's too little fluid, it's called oligohydramnios. According to the March of Dimes, about 8 percent of pregnant women have low levels of amniotic fluid at some point, usually in their third trimester. If this happens to you, your caregiver will follow your pregnancy closely to be sure your baby continues to grow normally. If you're near the end of your pregnancy, labor will be induced.

Read more about what it means to have low amniotic fluid, and the signs your doctor or midwife may look for.

Preeclampsia

Preeclampsia is a complex disorder that affects 3 to 8 percent of pregnant women. It's diagnosed when a woman, after 20 weeks of pregnancy, has two symptoms at once: newly elevated blood pressure and protein in her urine. Most expectant mothers who get preeclampsia develop a mild version near their due date, and they and their babies do fine with proper care. But severe preeclampsia can affect many organs and cause serious or even life-threatening problems. Moms whose preeclampsia is severe or getting worse need to deliver early.

Read more about how preeclampsia could affect your health and the health of your baby.