Patient education: When your baby is measuring small during pregnancy (The Basics)

How is a baby's growth measured during pregnancy? — This can be done in a few different ways.

Normally, pregnancy lasts about 40 weeks, counting from the first day of your last period. Doctors use the term "gestational age" to tell how far along the pregnancy is. For example, if you are 20 weeks pregnant, your baby's gestational age is 20 weeks. By knowing the gestational age, your doctor or midwife can estimate your "due date" and plan your care. It also helps them figure out if the baby is growing as expected.

Ways to check your baby's growth include:

●Ultrasound (figure 1) – This is an imaging test that creates pictures of the fetus (developing baby). An ultrasound is usually done early in pregnancy to help figure out the gestational age. Later in pregnancy, it is sometimes done to check how the baby is growing. The person who does the ultrasound can take measurements of specific parts of the baby's body. These usually include the head, belly, and femur (thigh bone).

●Feeling or measuring your belly – Your doctor or midwife can feel your belly from different angles. This helps them get an idea of the size of the fetus. They might also measure your belly, usually from the top of your uterus to your pubic bone (figure 2). Then, they can see how it grows over time.

These ways of measuring can give an estimate of your baby's size and weight. This can be compared with the average size and weight for babies of the same gestational age.

What does it mean if my baby is measuring small? — Doctors use the term "small for gestational age" when a fetus is measuring very small. This usually means smaller than 90 percent of babies of the same gestational age. This does not always mean that there is a problem. Many babies are small but still develop normally. For example, if you are very small in size, you are more likely to have a baby that is also small.

Some babies who are measuring small have something called "fetal growth restriction." This is when there is a problem preventing them from growing the way that they should. Different things can increase the risk of this. Examples include:

●A genetic problem

●Infection in the baby

●A problem with the placenta

●A problem with how the baby is developing

●Certain medical conditions in the mother

●Drinking alcohol, smoking, using drugs, or taking certain medicines during pregnancy

●Having more than 1 baby at once (such as twins or triplets)

Will I need tests? — Yes. If your baby is measuring small during pregnancy, you will probably have more tests. These can help your doctor figure out if there is a problem.

Tests might include:

●More ultrasounds – These can be used to measure how the fetus grows over time. They also let your doctor or midwife measure your amniotic fluid and look at your placenta.

●Other imaging tests to check blood flow in the umbilical cord or in the baby's brain

●Tests to check the baby's heart rate, movement, or breathing

What happens during and after birth? — Depending on your situation and your test results, your doctor might want you to give birth before your due date. That's because in some cases, if a baby is not growing normally, it could be at risk for stillbirth. (Stillbirth is when a baby dies before it is born.) If your doctor recommends having your baby earlier than 34 weeks of pregnancy, they can give medicine to help the baby's lungs develop faster.

Babies born very small have a higher risk of problems right after birth. This is more likely if they were also born early or if their brain did not get enough oxygen before, during, or after birth. Possible problems include:

●Low blood sugar

●Low blood calcium

●Trouble staying warm

●High red blood cell count

●Heart and breathing problems

●Weak muscle tone

When your baby is born, the medical team will be prepared to care for them and treat any problems. The baby might need to go to the neonatal intensive care unit, or "NICU." This is a part of the hospital for babies who need special care.

Will my baby have long-term problems? — It depends. Some babies catch up in size as they get older. Babies that are born very small often continue to be shorter and weigh less than other children. They also have a higher risk for:

●Learning problems in childhood

●Heart problems, high blood pressure, and kidney disease as adults

It is not always possible to know if a child will have these or other problems. Your child's doctor can work with you to make sure they get the treatment and help they need.

Is there anything I can do to help my baby grow normally? — Yes. In general, you can improve your chances of having a healthy pregnancy by going to all of your prenatal appointments. Follow your doctor's or midwife's instructions around taking care of yourself and your body.

To lower the risk of having a baby that is very small:

●Do not smoke, especially during pregnancy. If you are trying to quit, your doctor or nurse can help.

●Do not drink alcohol during pregnancy.

●If you have had problems with a past pregnancy, tell your doctor or midwife. They might want to do extra tests or schedule extra appointments.

More on this topic

Patient education: When your baby is measuring large during pregnancy (The Basics)
Patient education: Abdominal ultrasound (The Basics)
Patient education: What to expect in the NICU (The Basics)
Patient education: Stillbirth (The Basics)
Patient education: Having twins (The Basics)
Patient education: Labor and childbirth (The Basics)
Patient education: Prenatal care (The Basics)
Patient education: Nutrition before and during pregnancy (The Basics)