Risk Factors for Preterm Birth

Your Baby
Weeks 5 to 9

Your baby is about 1 to 2 inches long. All major organs are present. Although still developing, his eyelids and tongue have formed, as well as his ears and face. His arms and legs look like “flippers” with short, stubby buds that become hands and feet with rays that become fingers and toes. His knees and ankles begin forming. The spinal cord and nervous system begin to develop. His head is twice as large as the rest of his body because his brain grows faster than other organs. His heart is beating twice as fast as yours as it pumps blood to the placenta. Your blood must carry oxygen and folic acid to the placenta to help your baby’s brain and spinal cord develop normally. His liver is larger than his other organs so your baby looks like he has a potbelly.

Even if you have risk factors, an early birth can often be prevented or delayed if symptoms of preterm labor are detected early and treated. Even if you have risk factors, an early birth can often be prevented or delayed if symptoms of preterm labor are detected early and treated. Known risk factors include the health history of your family and your personal health history. While these risk factors can’t be changed, it is important to be aware of them. They are part of your risk for preterm birth. Your risk factors are unique to you. What may be a risk factor for you may have little effect on another mother. The more risk factors you have, the higher your chance of preterm labor. Therefore, it is important that you learn which risk factors affect you; then do what you can to reduce your risk. Knowing that you have risk factors you can’t change should encourage you to reduce the risk factors that you can change.

Race and Ethnic Background

The risks linked to race and ethnic background are hard to measure because they are a combination of biology and culture. In the United States, statistics show that African-American mothers are at the highest risk for preterm birth, followed by Hispanic and Caucasian mothers. Asian mothers have the lowest risk.


If you are younger than 18 or over 35 – and this is your first pregnancy – your risk for preterm birth is increased. The reasons are different for each age group.

Under 18

Preemie boy in incubaorPart of the risk for mothers under 18 and their babies is poor nutrition. Many teenage mothers are still growing. Both mother and unborn baby must compete for available calories and nutrients that they each need to grow. Poor nutrition during pregnancy can result in a baby that is born too soon and too small. Nutrition, particularly the rate and amount of weight gain, is important for teenage mothers and their babies.

Also, teen mothers are often dealing with financial, social, and emotional issues and don’t seek prenatal care early enough. It is better for you and your baby if prenatal care begins as soon as you think you are pregnant. The earlier prenatal care begins, the sooner problems can be found and treated. Early treatment reduces health problems for both mother and baby.

Over 35

More and more women are putting off having children because of career choices, education, marriage, or financial reasons. The risks linked to pregnancy after 35 are less for mothers in good health. However, if you are over 35, you are more likely to have a health condition, such as heart disease, diabetes, or high blood pressure, which can increase your risk for preterm birth.

In addition, mothers over 35 are more likely to have had a previous preterm birth, abortion, or other obstetrical or gynecological condition. These factors increase the risk for preterm birth with this pregnancy.

The risks linked to pregnancy after 35 can be reduced by getting prenatal care early, controlling any health problems you have, and controlling risk factors such as mental and physical stress and risks linked to lifestyle, such as smoking, using alcohol or drugs.

Size and Makeup of Household

Single mothers are at increased risk for preterm birth. Single mothers, especially those without help, must handle all the physical, emotional, and financial stresses of raising a family alone. Stress everyday can increase the overall risk for preterm birth.

Because of the amount of physical effort in a single mother’s daily life, her risk is further increased if she has young children, more than two children, or an elderly relative living with her or depending on her for care.

Gynecological, Obstetrical, and Health Factors

Each pregnancy has its own set of risk factors because you’re older with each pregnancy, and risk factors change with age.

Previous abortion or miscarriage

Your risk for preterm birth can be increased if a prior pregnancy ended in a miscarriage or an abortion. The length of your pregnancy when you miscarried can affect your risk now. The number of abortions also affects your risk.

Previous preterm birth

Preventing preterm birth is important not only for this pregnancy but also for future pregnancies. Mothers often have babies whose gestational age and birth weight are similar to those of a previous pregnancy. So your risk for preterm birth is greatly increased if you had a previous preterm birth. Keep in mind that even with a previous preterm birth, you may be able to reduce your risk in a future pregnancy by carrying this baby to full-term.

Your Mother took DES

If your mother was prescribed the drug diethylstilbestrol (DES) when she was pregnant with you, your risk for preterm birth is increased. DES was prescribed from 1940 to 1971 to prevent miscarriage. It causes physical changes in the uterus and cervix of the daughters.

Current Pregnancy

In addition to risk factors from a previous pregnancy, your current pregnancy can have risk factors to consider.

Current health status

Health conditions such as diabetes, high blood pressure, and heart disease—even if they are well controlled—add to your risk for preterm birth. These three health conditions cause changes in the structure of blood vessels and have been linked to slow growth rate in an unborn baby and preterm birth.

Infertility treatments

If your current pregnancy resulted from infertility treatments, your body has already been through a difficult process. Pregnancies that result from infertility treatments, particularly in vitro fertilization, are at risk for preterm birth. In addition, fertility drugs are more likely to produce multiple births. Multiple births greatly increase the risk of preterm labor.


Infection of the vagina, uterus, and urinary tract is often linked to preterm labor and preterm birth.

Infection of the Vagina and Uterus. Vaginal infections that go untreated can result in preterm birth. The most common cause of infection of the uterus is germs that get into the uterus through the vagina. To reduce the risk of infection of the uterus:
~ do not use any type of vaginal douche
~ use sanitary pads, not tampons for vaginal discharge. Tampons keep discharge inside the vagina and provide a place for germs to grow.
~ if you have symptoms of vaginal infection, call your doctor.

The symptoms of a vaginal infection include pain, itching, unusual discharge, or a bad smell. If you have symptoms of a vaginal infection, tenderness in your lower abdomen, or a fever over 100.4° F, call your doctor. The cause of the problem should be determined and treated right away.

Urinary tract infection. Urinary tract infections can cause activity in the uterus or premature rupture of the membranes and lead to preterm birth. To reduce your risk of urinary tract infection:
~ eat a balanced diet and drink plenty of water. Drinking cranberry juice has been shown to reduce urinary tract infections.
~ empty your bladder often
~ when you have to urinate, don’t hold it
~ use proper perineal hygiene (see below)
~ wear white, 100% cotton panties

The signs and symptoms of urinary tract infection are:
~ feeling like you have to urinate more often than usual
~ feeling like you “won’t make it to the bathroom in time”
~ blood in your urine
~ chills and fever
~ urine that smells bad or looks cloudy
~ pain in the middle of your back
~ increased pressure in your lower abdomen
~ pain or burning when you urinate

If you have symptoms of a urinary tract infection, call your doctor.

Proper perineal hygiene. After urination or a bowel movement, wipe yourself from front to back using white, unscented toilet paper. Use a clean piece of toilet paper for each stroke. Always wash your hands when you finish. Pregnancy causes an increase in vaginal discharge. It’s okay to wear panty shields or sanitary pads to protect your clothing. If you wear panty shields or sanitary pads, wash your hands before and after you change pads. Avoid dragging germs from the anal area to the vaginal area when taking off and putting on a sanitary pad. When opening or putting on a clean pad, don’t touch the side that goes against your body.

Preterm Birth Can’t Always Be Prevented

Some preterm births can’t be prevented. However, if mother and baby aren’t in danger, preterm birth can sometimes be delayed, which allows the baby more time to mature. The following are conditions that often result in preterm birth.

Twin girl preemies
Expecting more than one baby
Preterm birth is five times more likely for twins and almost nine times more likely for three or more babies. This is probably caused by the uterus being stretched so much. Reducing those risk factors you can control is important if you are expecting more than one baby. Low birth weight is often a result of preterm birth and is common among multiple births. Eating a healthy diet can help improve the growth, development, and birth weight of multiple babies.

Problems with the placenta or cervix
Slight bleeding can occur when the embryo implants itself in the lining of the uterus. Bleeding after the embryo implants is a warning sign that something can be wrong. If the embryo hasn’t implanted well or implanted in a poor location, the pregnancy will probably end early. Sometimes the pregnancy ends even before the mother knows she is pregnant. If the embryo implants near the cervix, bleeding is likely as the placenta grows.

The Placenta
The placenta is made of cells from you and cells from your baby. The placenta acts as your baby’s lungs, kidneys, and digestive system. Your baby is connected to the placenta by the umbilical cord. The umbilical cord is about the length of the fetus. The placenta increases in size and weight throughout your pregnancy until it weighs just over a pound and is about the size and shape of a pancake (6-8 inches across and 3/4 to 1 1/4 inches thick). The placenta usually attaches on the back side of the uterus, near the top (opposite the cervix) but it may attach lower.Your blood and your baby’s blood pass very close together, but there is no mixing of blood, or direct connection, only an exchange of gases and food across the placenta. The umbilical cord has two arteries and one vein which branch off to the placenta. To get oxygen and food, your baby pumps his blood through the umbilical cord to the placenta. Oxygen, sugar, fat, proteins, vitamins, and minerals are carried in your blood to the placenta. As your baby’s blood passes through, carbon dioxide and waste products are left behind and food and oxygen are picked up and taken back through the umbilical cord for his body to use for energy and growth. The placenta is how your baby “breathes”, gets nutrition and removes waste. After your baby is born, the placenta separates from the uterus and is expelled as after-birth. Although the blood vessels are torn with the separation, firm contractions in the uterus, called after pains, close off the vessels and prevent hemorrhage.

Problems with the placenta increase the risk for preterm birth and can become an emergency situation for both mother and baby. Placenta previa is when the placenta covers all or part of the cervix and detaches from the uterus as the cervix opens. Painless, bright-red bleeding from the vagina after the first trimester can be an early warning sign of placenta previa.

If the placenta detaches from the uterus, called abruptio placentae, the oxygen supply to the baby is suddenly reduced and the baby must be delivered right away, often by cesarean before full-term. Bleeding and sharp abdominal pain that feels like one long contraction can be symptoms of abruptio placentae.

Incompetent cervix is when the cervix begins to open, painlessly, weeks or months before full-term. The bag of waters can bulge through the cervix and preterm labor can begin. The cervix may have been weakened due to previous miscarriage, preterm labor, or D&C.

A thick mucous discharge can be a symptom of incompetent cervix that may be present in early pregnancy. As pregnancy progresses, some mothers begin feeling pressure in the pelvis, menstrual-like cramps, or a low backache. Since incompetent cervix can be very serious, even the slightest symptoms should not be ignored. If incompetent cervix is detected early enough, the cervix can be sewn together, called cerclage. The mother can then stay on bed rest until fullterm when the stitches are removed.

Premature Rupture of the Membranes (PROM)

During pregnancy, the baby floats in fetal membranes, called “bag of waters”, filled with amniotic fluid which protects the baby and the umbilical cord. If the bag of waters breaks before full-term, the risks of preterm birth and infection are greatly increased. Although some fluid is lost, the baby continues to make more, which can continue to leak. If the bag of waters is leaking, you may notice your panties are always wet or damp. With PROM a mother may need to be in the hospital where she and her baby can be watched carefully and her healthcare team can respond quickly to changes that can lead to problems. Usually, the closer a mother is to her due date, the sooner labor is likely to begin once the membranes rupture.

To Learn More about Preventing Preterm Birth

To Learn More about Caring for Your Newborn