Pregnancy

Definition

Pregnancy is a period of up to 41 weeks in which a fetus develops inside a woman’s womb. NICHD conducts and supports research and training to help promote healthy pregnancies, with a focus on the important events that occur before, during, and after pregnancy.

Pregnancy is the term used to describe the period in which a fetus develops inside a woman’s womb or uterus.

Pregnancy usually lasts about 40 weeks, or just over 9 months, as measured from the last menstrual period to delivery. Healthcare providers refer to three segments of pregnancy, called trimesters.

Symptoms

The primary sign of pregnancy is missing a menstrual period or two or more consecutive periods, but many women experience other symptoms of pregnancy before they miss a period.

Missing a period does not always mean a woman is pregnant. Menstrual irregularities are common and can have a variety of causes, including taking birth control pills, conditions such as diabetes and polycystic ovary syndrome, eating disorders, and certain medications. Women who miss a period should see their healthcare provider to find out whether they are pregnant or whether they have another health problem.

Pregnancy symptoms vary from woman to woman. A woman may experience every common symptom, just a few, or none at all. Some signs of early pregnancy include:

• Slight bleeding. One study shows as many as 25% of pregnant women experience slight bleeding or spotting that is lighter in color than normal menstrual blood. This typically occurs at the time of implantation of the fertilized egg (about 6 to 12 days after conception) but is common in the first 12 weeks of pregnancy.
• Tender, swollen breasts or nipples. Women may notice this symptom as early as 1 to 2 weeks after conception. Hormonal changes can make the breasts sore or even tingly. The breasts feel fuller or heavier as well.
• Fatigue. Many women feel more tired early in pregnancy because their bodies are producing more of a hormone called progesterone, which helps maintain the pregnancy and encourages the growth of milk-producing glands in the breasts. In addition, during pregnancy the body pumps more blood to carry nutrients to the fetus. Pregnant women may notice fatigue as early as 1 week after conception.
• Headaches. The sudden rise of hormones may trigger headaches early in pregnancy.
• Nausea and/or vomiting. This symptom can start anywhere from 2 to 8 weeks after conception and can continue throughout pregnancy. Commonly referred to as “morning sickness,” it can actually occur at any time during the day.
• Food cravings or aversions. Sudden cravings or developing a dislike of favorite foods are both common throughout pregnancy. A food craving or aversion can last the entire pregnancy or vary throughout this period.
• Mood swings. Hormonal changes during pregnancy often cause sharp mood swings. These can occur as early as a few weeks after conception.
• Frequent urination. The need to empty the bladder more often is common throughout pregnancy. In the first few weeks of pregnancy, the body produces a hormone called human chorionic gonadotropin, which increases blood flow to the pelvic region, causing women to have to urinate more often.

Many of these symptoms can also be signs of other conditions, the result of changing birth control pills, or effects of stress, so they do not always mean that a woman is pregnant. Women should see their healthcare provider if they suspect they are pregnant.

Trimesters

First Trimester (Week 1 to Week 12)

The events that lead to pregnancy begin with conception, in which a sperm penetrates an egg. The fertilized egg (called a zygote) then travels through the woman’s fallopian tube to the uterus, where it implants itself in the uterine wall. The zygote is made up of a cluster of cells that later form the fetus and the placenta. The placenta connects the mother to the fetus and provides nutrients and oxygen to the fetus.

Second Trimester (Week 13 to Week 28)

• Between 18 and 20 weeks, the typical timing for ultrasound to look for birth defects, you can often find out the sex of your baby.
• At 20 weeks, a woman may begin to feel movement.
• At 24 weeks, footprints and fingerprints have formed and the fetus sleeps and wakes regularly.
• According to research from the NICHD Neonatal Research Network, the survival rate for babies born at 28 weeks was 92%, although those born at this time will likely still experience serious health complications, including respiratory and neurologic problems.

Third Trimester (Week 29 to Week 40)

• At 32 weeks, the bones are soft and yet almost fully formed, and the eyes can open and close.
• Infants born before 37 weeks are considered preterm. These children are at increased risk for problems such as developmental delays, vision and hearing problems, and cerebral palsy. Infants born between 34 and 36 weeks of pregnancy are considered to be “late preterm.”
• Infants born in the 37th and 38th weeks of pregnancy—previously considered term—are now considered “early term.” These infants face more health risks than infants who are born at 39 weeks or later, which is now considered full-term.
• Infants born at 39 or 40 weeks of pregnancy are considered full-term. Full-term infants have better health outcomes than infants born earlier or, in some cases, later than this period. Therefore, if there is no medical reason to deliver earlier, it is best to deliver at or after 39 weeks to give the infant’s lungs, brain, and liver time to fully develop.
• Infants born at 41 weeks through 41 weeks and 6 days are considered late term.
• Infants who are born at 42 weeks and beyond are considered post-term.

Prenatal Care

Having a healthy pregnancy is one of the best ways to promote a healthy birth. Getting early and regular prenatal care improves the chances of a healthy pregnancy. This care can begin even before pregnancy with a pre-pregnancy care visit to a health care provider.

Pre-Pregnancy Care

A pre-pregnancy care visit can help women take steps toward a healthy pregnancy before they even get pregnant. Women can help to promote a healthy pregnancy and birth of a healthy baby by taking the following steps before they become pregnant:

• Develop a plan for their reproductive life.
• Increase their daily intake of folic acid (one of the B vitamins) to at least 400 micrograms.²
• Make sure their immunizations are up to date.
• Control diabetes and other medical conditions.
• Avoid smoking, drinking alcohol, and using drugs.
• Attain a healthy weight.
• Learn about their family health history and that of their partner.
• Seek help for depression, anxiety, or other mental health issues.

Prenatal Care

Women who suspect they may be pregnant should schedule a visit to their healthcare provider to begin prenatal care. Prenatal visits to a health care provider usually include a physical exam, weight checks, and providing a urine sample. Depending on the stage of the pregnancy, healthcare providers may also do blood tests and imaging tests, such as ultrasound exams. These visits also include discussions about the mother’s health, the fetus’s health, and any questions about the pregnancy.

Pre-pregnancy and prenatal care can help prevent complications and inform women about important steps they can take to protect their infants and ensure a healthy pregnancy. With regular prenatal care, women can:

• Reduce the risk of pregnancy complications. Following a healthy, safe diet; getting regular exercise as advised by a health care provider; and avoiding exposure to potentially harmful substances such as lead and radiation can help reduce the risk for problems during pregnancy and promote fetal health and development. Controlling existing conditions, such as high blood pressure and diabetes, is important to prevent serious complications and their effects.
• Reduce the fetus’s and infant’s risk for complications. Tobacco smoke and alcohol use during pregnancy have been shown to increase the risk of Sudden Infant Death Syndrome. Alcohol use also increases the risk for fetal alcohol spectrum disorders, which can cause a variety of problems such as abnormal facial features, having a small head, poor coordination, poor memory, intellectual disability, and problems with the heart, kidneys, or bones. According to one recent study supported by the NIH, these and other long-term problems can occur even with low levels of prenatal alcohol exposure.

In addition, taking 400 micrograms of folic acid daily reduces the risk for neural tube defects by 70%. Most prenatal vitamins contain the recommended 400 micrograms of folic acid as well as other vitamins that pregnant women and their developing fetus need. Folic acid has been added to foods like cereals, breads, pasta, and other grain-based foods. Although a related form (called folate) is present in orange juice and leafy, green vegetables (such as kale and spinach), folate is not absorbed as well as folic acid.

Women should not take certain medications, including some acne treatments and dietary and herbal supplements, during pregnancy because they can harm the fetus.

Complications

Getting early and regular prenatal care can help decrease the risk for problems by enabling healthcare providers to diagnose, treat, or manage conditions before they become serious. Prenatal care can also help identify mental health concerns related to pregnancy, such as anxiety and depression.

Some common complications of pregnancy include, but are not limited to, the following.

High Blood Pressure

High blood pressure, also called hypertension, occurs when arteries carrying blood from the heart to the body organs are narrowed. This causes pressure to increase in the arteries. In pregnancy, this can make it hard for blood to reach the placenta, which provides nutrients and oxygen to the fetus. Reduced blood flow can slow the growth of the fetus and place the mother at greater risk of preterm labor and preeclampsia.

Women who have high blood pressure before they get pregnant will continue to have to monitor and control it, with medications if necessary, throughout their pregnancy. High blood pressure that develops in pregnancy is called gestational hypertension. Typically, gestational hypertension occurs during the second half of pregnancy and goes away after delivery.

Gestational Diabetes

Gestational diabetes occurs when a woman who didn’t have diabetes before pregnancy develops the condition during pregnancy.

Normally, the body digests parts of your food into a sugar called glucose. Glucose is your body’s main source of energy. After digestion, the glucose moves into your blood to give your body energy.

To get the glucose out of your blood and into the cells of your body, your pancreas makes a hormone called insulin. In gestational diabetes, hormonal changes from pregnancy cause the body to either not make enough insulin, or not use it normally. Instead, the glucose builds up in your blood, causing diabetes, otherwise known as high blood sugar.

Managing gestational diabetes, by following a treatment plan outlined by a healthcare provider, is the best way to reduce or prevent problems associated with high blood sugar during pregnancy. If not controlled, it can lead to high blood pressure from preeclampsia and having a large infant, which increases the risk for cesarean delivery.

Infections

Infections, including some sexually transmitted infections (STIs), may occur during pregnancy and/or delivery and may lead to complications for the pregnant woman, the pregnancy, and the baby after delivery. Some infections can pass from mother to infant during delivery when the infant passes through the birth canal; other infections can infect a fetus during the pregnancy.¹ Many of these infections can be prevented or treated with appropriate pre-pregnancy, prenatal, and postpartum follow-up care.

Some infections in pregnancy can cause or contribute to:

• Pregnancy loss/miscarriage (before 20 weeks of pregnancy)
• Ectopic pregnancy (when the embryo implants outside of the uterus, usually in a fallopian tube)
• Preterm labor and delivery (before 37 completed weeks of pregnancy)
• Low birth weight
• Birth defects, including blindness, deafness, bone deformities, and intellectual disability
• Stillbirth (at or after 20 weeks of pregnancy)
• Illness in the newborn period (first month of life)
• Newborn death
• Maternal health complications

If you are planning to get pregnant, talk with your healthcare provider about getting vaccines and vaccine boosters for chicken pox (also called varicella) and rubella (also called German measles) before you conceive. You can also get some vaccines, such as the flu shot, while you are pregnant. If you know you have an infection, such as an STI, talk with your healthcare provider about it before you conceive to increase your chances of a healthy pregnancy.

Early prenatal testing for STIs and other infections can determine if the infection can be cured with drug treatment. Or, if you know you have an infection, tell your pregnancy healthcare provider about it as early as possible in your pregnancy. Early treatment decreases the risk to the fetus and infant. Even if the infection can’t be cured, you and your healthcare provider can take steps to protect your health and your infant’s health.

Preeclampsia

Preeclampsia is a serious medical condition that can lead to preterm delivery and death. Its cause is unknown, but some women are at an increased risk. Risk factors include:

• First pregnancies
• Preeclampsia in a previous pregnancy
• Existing conditions such as high blood pressure, diabetes, kidney disease, and systemic lupus erythematosus
• Being 35 years of age or older
• Carrying two or more fetuses
• Obesity

Preterm Labor

Preterm labor is labor that begins before 37 weeks of pregnancy. Any infant born before 37 weeks is at an increased risk for health problems, in most cases because organs such as the lungs and brain finish their development in the final weeks before a full-term delivery (39 to 40 weeks).

Certain conditions increase the risk for preterm labor, including infections, developing a shortened cervix, or previous preterm births.