Late-term and postterm pregnancy: Clinical sciences

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Introduction0:00–1:43

Late-term and postterm pregnancies occur when a pregnancy continues beyond the standardized 40 weeks of gestation. More specifically, late-term refers to those pregnancies at or beyond 41 weeks of gestation and postterm refers to pregnancies at or beyond 42 weeks of gestation.
Both are associated with increased risks of maternal and fetal morbidity and mortality. Intrapartum risks are related to an increased incidence of oligohydramnios, which is a decreased amniotic fluid that’s associated with umbilical cord compression, fetal heart rate abnormalities, and meconium-stained fluid.
When it comes to delivery risks, there is an increased risk of operative-assisted vaginal deliveries or c-section deliveries, shoulder dystocia, severe perineal lacerations, and postpartum hemorrhage.
Now, there are also some neonatal risks as well, such as meconium aspiration syndrome, neonatal convulsions, 5-minute Apgar scores of less than 4, and increased rates of NICU admissions.
Finally, while the absolute risk is low, the risk of stillbirth increases with each subsequent week of gestation after week 40.
Thus, it is important to accurately identify late-term and postterm pregnancies, categorize pregnancies into high and low-risk states, and initiate appropriate antenatal testing once a patient enters this stage of gestation.
When a patient presents with a late-term or postterm pregnancy, you should start with a focused history and physical exam.

History and physical1:43–2:28

History might reveal some associated risk factors for late-term and postterm pregnancy including nulliparity, a history of a prior late-term or postterm pregnancy, carrying a male fetus, and certain fetal disorders in the current pregnancy, such as anencephaly.
On physical exam, you may note a BMI of 30 or more, as obesity is a risk factor for prolonged pregnancy. Additionally, the dating of the pregnancy will be confirmed to be at least 39 and 0/7 weeks of gestation.Now that you have obtained some helpful information, your next step is to determine if your patient has a high or low-risk pregnancy.

High vs low-risk2:28–3:42

This is important because patients with high-risk pregnancies require additional antenatal monitoring. Also, they will likely need to be delivered by their estimated due date, or by 40 weeks of gestation, to decrease associated maternal, fetal, and neonatal risks.
Some factors that classify a pregnancy as high risk include advanced maternal age, or AMA; pregnancy as a result of in-vitro fertilization or IVF; fetal disorders, such as anencephaly; hypertensive disorders of pregnancy like preeclampsia; gestational diabetes; intrauterine growth restriction or IUGR; maternal illness such as lupus, and renal or thyroid disease; a history of prior stillbirth; and placental disorders such as polyhydramnios, oligohydramnios, or a single umbilical artery.Okay, if your patient has a high-risk pregnancy, initiate regular third trimester antenatal testing, which is performed to assess fetal well-being.

High-risk3:42–6:22

Antenatal testing may include non-stress tests, or NSTs; assessment of amniotic fluid index, also known as AFI; biophysical profiles, or BPPs; and growth ultrasounds.
The frequency of antenatal testing varies for each patient but ranges from once per week to multiple times each week. Now, non-reassuring testing may include non-reactive NST or a fetal heart tracing with decelerations on an NST; polyhydramnios or oligohydramnios on AFI measurement; a low BPP score; or inadequate fetal growth on ultrasound.
If at any point after 39 weeks of gestation the testing is non-reassuring, you should proceed with delivery. Delivery is completed either by induction of labor or c-section for those with contraindications to vaginal delivery.
On the flip side, reassuring antenatal testing will show reactive NSTs with moderate variability and accelerations; normal AFI measurement; a reassuring BPP and adequate fetal growth on ultrasound.
In this situation, as you are dealing with a term pregnancy, you can allow it to continue beyond 39 weeks. For these patients, you should plan for delivery by 40 weeks and 0 days to minimize the increased risk of morbidity to both the mother and the baby.
Again, this can be either by induction of labor or scheduled c-section. Here’s a clinical pearl!
Patients with high-risk pregnancies generally complete antenatal testing starting between 32 to 36 weeks of gestation. If at any point antenatal testing becomes non-reassuring, consideration for the risks of premature birth versus the benefits of pregnancy continuation should be weighed.
The reason non-reassuring testing after 39 weeks of gestation prompts delivery is that fetuses are fully formed and there are minimal, if any, benefits to pregnancy continuation with nonreassuring antenatal testing at this gestational age.
Alright, now that high-risk patients are taken care of, let’s go back a step and talk about patients with low-risk pregnancies.

Low risk6:22–9:33

For these patients, pregnancy could be continued without intervention until late-term gestation, or between 41 weeks and 0 days to 41 weeks and 6 days of gestation.
That being said, antenatal testing is recommended starting at 41 weeks and 0 days of gestation due to the sharp increased risk of stillbirth that occurs at this time.
Here’s another clinical pearl! In practice, most providers will recommend starting antenatal testing in a low-risk pregnancy at 40 weeks of gestation, via a NST and AFI.Okay, let’s return to your patient.
Next, assess if the antenatal testing is reassuring or non-reassuring. If it is non-reassuring, proceed with delivery.
However, if the testing is reassuring, your patient may choose to continue their pregnancy through the duration of the late-term period, or until 41 weeks and 6 days of gestation.
Patients may choose this option if they strongly desire spontaneous labor or for other personal reasons. Regardless, be sure to counsel them on awareness of reduced fetal movement, or a decrease in the frequency or strength of fetal movements; and continue antenatal testing.
Currently, there is no consensus on how often this testing should be performed, but most providers will opt for non-stress testing 2 to 3 times a week.
If at any point the testing is non-reassuring, you should proceed with delivery. Alternatively, if the testing is reassuring, your patient may continue their pregnancy without intervention until postterm gestation, or greater than or equal to 42 weeks and 0 days.
Generally, the recommendation is for delivery by 42 weeks, even in low-risk pregnancies, because the rate of stillbirth is significantly increased.
That being said, some patients may decide to continue their pregnancy and await spontaneous labor, in which case careful consideration for pregnancy continuation should be discussed.
Delivery is absolutely recommended by 42 weeks and 6 days of gestation, as pregnancies at or beyond 43 weeks are associated with an unacceptably high risk of stillbirth.
Here’s a final clinical pearl! While it’s safe to continue low-risk pregnancies until 42 weeks 6 days of gestation if antenatal testing remains reassuring, the option for an elective induction of labor also exists!
So, you could offer pregnancy continuation OR elective induction for low-risk patients once they reach 39 weeks. Alright, as a quick recap… Late- and postterm pregnancy refers to pregnancies that have extended beyond the expected gestational period of 40 weeks.

Review9:33–10:17

High-risk pregnancies require third trimester antenatal testing. If testing is non-reassuring, delivery is generally recommended, whereas with reassuring results, delivery by 40 weeks is the goal.
On the flip side, low-risk pregnancies can continue to the late- or postterm period, so long as antenatal testing remains reassuring.
When delivery is indicated, vaginal delivery is preferred unless obstetric contraindications to a vaginal delivery exist, in which case a c-section is recommended.