Definition

Postterm pregnancy is a pregnancy that lasts more than 42 weeks from the first day of the last menstrual period (LMP).

Although pregnancy is typically said to last for 9 months, doctors measure gestational age in weeks and days. The estimated due date is calculated as 40 weeks or 280 days from the LMP. Only 4% (1 in 20) of pregnant women will give birth on their estimated due date.

The normal duration of pregnancy ranges between 37 and 42 weeks, referred to as term pregnancy. A pregnancy between 41 and 42 weeks is called late-term.

Most women give birth between 37 and 42 weeks of pregnancy. About 10% of pregnant women will give birth postterm.

Causes

The most common cause of postterm pregnancy is an error in calculating the estimated due date (EDD). In accurately calculated pregnancies, the cause of postterm pregnancy is usually unknown.

Accurate determination of gestational age is crucial to confirm that a pregnancy is truly postterm. Ideally, accurate gestational age is determined early in pregnancy. In women with regular menstrual cycles, gestational age can be estimated quite accurately based on LMP and physical examination.

In women with long or irregular menstrual cycles, variations in ovulation timing can lead to errors in estimating gestational age and EDD based on LMP. This can result in an EDD that is too early or late.

If the menstrual cycle is irregular, or there is uncertainty about the LMP, or if the size of the uterus is larger or smaller than expected based on the LMP, gestational age and EDD are better estimated using ultrasound. This estimation is most accurate when performed early in pregnancy (up to 20 weeks of gestation). Ultrasound done later in pregnancy is less accurate in estimating the EDD.

Risk Factor

Several factors increase the risk of postterm pregnancy, including:

• First pregnancy
• Previous postterm pregnancy
• Genetic factors. A study showed an increased risk of post-term pregnancy in pregnant women who were themselves born postterm.

Symptoms

Characteristics of the Baby

There are no symptoms in postterm pregnancy. However, postterm babies may have characteristics such as:

• Less fat under the skin, leading to looser skin
• Dry and cracked skin
• Longer fingernails, which may be stained yellow from fetal stool (meconium)

Characteristics of the Mother

Signs the mother may notice include:

• Decreased fetal movement
• Decreased size of the fetus due to a reduction in amniotic fluid volume
• Amniotic fluid mixed with meconium, visible when the amniotic sac ruptures and fluid flows out

Diagnosis

To calculate the EDD, doctors may:

• Measure the size of the uterus at specific times during early pregnancy
• Record the day when the fetal heartbeat is first heard
• Record the day when the mother first feels fetal movement
• Use ultrasound

In post-term pregnancy, doctors may perform tests to check the fetus's health and identify any issues. These tests include:

• Ultrasound
• Fetal heart rate monitoring
• Measuring the amount of amniotic fluid

If you want to learn about one of the indicators of labor, which is premature rupture of membranes, you may read it here.: Early Burst Of Bursts - Definition, Cause, Symptoms, And Treatment

Management

The goal of managing postterm pregnancy is to prevent complications and deliver a healthy baby. The doctor will recommend treatment based on the pregnancy, your age, and your overall health. The severity of your condition will also be considered.

Doctors may perform tests on the mother and fetus to identify any problems. These tests include:

• Fetal movement counting: To monitor the fetus's movements and kicks. Changes in frequency or number may indicate fetal distress.
• Non-stress testing: This test observes how the fetal heart rate increases when the fetus moves, indicating fetal health.
• Biophysical profile: A combination of a non-stress test and ultrasound to assess fetal health.
• Obstetric ultrasound: This test uses high-frequency sound waves and a computer to create images of blood vessels, tissues, and organs. Ultrasound also monitors fetal growth.
• Doppler flow study: A type of ultrasound that uses sound waves to measure blood flow, often used if the fetus is not growing normally.

If the tests indicate that the fetus may not thrive if it remains in the womb, the doctor may induce labor. During labor, the doctor will monitor the fetal heart rate electronically to detect any changes caused by low oxygen levels. If the fetus's condition worsens, a cesarean delivery may be necessary.

Complications

A pregnancy that continues beyond 42 weeks is associated with risks for both the fetus and the mother.

Fetal Risks

• Stillbirth or newborn death: The risk of stillbirth or newborn death increases in pregnancies beyond 42 weeks, but the risk is relatively small, with 4–7 deaths per 1,000 births. In comparison, the risk during 37-42 weeks is 2-3 per 1,000 births.
• Large fetal size: Post-term fetuses usually continue to grow past the EDD, increasing the risk of complications related to large body size and macrosomia, where the baby weighs more than 4,000 grams. Complications can include prolonged labor, difficulty passing through the birth canal, and birth trauma (such as fractures or nerve injuries) due to shoulder dystocia.
• Fetal dysmaturity: Some post-term fetuses stop growing after the EDD. Fetal dysmaturity, or postmaturity syndrome, occurs when the fetus's weight gain ceases after the EDD, usually due to impaired blood flow to the fetus through the placenta, leading to malnutrition. After birth, these babies may appear different, with long, thin limbs, dry or peeling skin, meconium staining, and sagging skin, especially on the thighs and buttocks. The scalp hair may be longer or thicker, and the nails may be long. However, some studies suggest that the growth, development, and intelligence of post-term and term babies are generally the same.
• Meconium aspiration: Post-term fetuses are more likely to pass stool (meconium) into the amniotic fluid. If the fetus experiences distress, it may inhale meconium-stained amniotic fluid, causing breathing problems after birth.

Maternal Risks

The risk to the mother is related to the larger size of the fetus postterm. These risks include:

• Difficult labor
• Injury to the perineum, vagina, vaginal lips, and rectum during normal delivery
• Possible need for cesarean section

Prevention

The primary way to prevent postterm pregnancy is to induce labor before 42 weeks. However, there are complications with this procedure, so doctors usually recommend waiting for spontaneous labor until 40 weeks.

Tips to speed up labor include doing sexual intercourse without condoms. You can also discuss with your doctor the option of manually separating the amniotic sac from the lower uterine wall.

When to See a Doctor?

Once your pregnancy reaches 37 weeks, you should have weekly prenatal checkups. It is crucial to keep these appointments. However, if you reach 42 weeks without signs of labor, such as contractions, fluid leakage from the vagina, and/or blood-tinged mucus discharge from the vagina, consult your doctor immediately.

Contact your doctor right away if:

• Your amniotic sac ruptures and fluid flows out
• You experience vaginal bleeding
• You notice changes in fetal activity levels

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