PTD stands for preterm delivery, meaning a baby is born before 37 weeks of pregnancy. In the United States, about 1 in 10 babies arrives preterm, with the rate holding steady at 10.41% in both 2023 and 2024. While many preterm babies grow up healthy, being born too early increases the risk of breathing problems, developmental delays, and other complications, especially the earlier delivery occurs.
Categories of Preterm Delivery
Not all preterm births carry the same level of risk. The World Health Organization breaks PTD into three categories based on how early the baby arrives:
- Extremely preterm: before 28 weeks
- Very preterm: 28 to less than 32 weeks
- Moderate to late preterm: 32 to 37 weeks
Most preterm births fall into the moderate to late preterm range. Babies born in this window generally need less intensive care and have better outcomes than those born earlier, though they still face higher risks than full-term infants. Extremely preterm babies, born before 28 weeks, face the most serious health challenges because their organs have had the least time to develop.
What Raises the Risk
Some pregnancies carry a higher chance of preterm delivery than others. The strongest single predictor is having had a previous preterm birth. Beyond that, several factors increase risk:
- Carrying multiples: twins, triplets, or more put extra strain on the uterus and often lead to earlier delivery
- Infections: urinary tract infections, bacterial vaginosis, and even COVID-19 during pregnancy are linked to PTD
- High blood pressure conditions: preeclampsia and other blood pressure disorders sometimes require early delivery to protect the mother’s health
In many cases, though, preterm labor starts without a clear cause. A short cervix, detected on ultrasound in the second trimester, is one of the most reliable physical warning signs that delivery may come early.
Warning Signs of Preterm Labor
Recognizing preterm labor early gives you the best chance of getting treatment that can delay delivery. The key symptoms to watch for include contractions or stomach tightening every 10 minutes or more often, a change in vaginal discharge (especially leaking fluid or bleeding), and a feeling of pressure low in the pelvis. Six or more contractions in a single hour is not normal and warrants immediate medical attention.
These symptoms can be subtle, and some women mistake early contractions for general discomfort. The difference is the regularity. If the tightening comes in a pattern and doesn’t ease up when you change positions or rest, that’s a sign your body may be moving toward labor.
How PTD Is Predicted
When a woman shows possible signs of preterm labor, one common test checks for a protein called fetal fibronectin in vaginal secretions. This protein acts like a biological glue between the amniotic sac and the uterine lining. Its presence after 22 weeks can signal that the body is preparing for delivery.
The test is most useful for its negative result. If fetal fibronectin is absent, the chance of delivering within the next week or two is very low, with a negative predictive value above 90% in most studies. A positive result is less definitive, since many women who test positive still carry to term, but it helps doctors decide whether to start protective treatments.
Treatments That Help Delay or Prepare for PTD
When preterm delivery looks likely, the medical team focuses on two goals: buying time for the baby to develop further and preparing the baby’s body for life outside the womb.
Progesterone
For women with a short cervix discovered on ultrasound between 20 and 25 weeks, vaginal progesterone can reduce the chance of preterm birth. It’s typically given daily from around 24 weeks until 36 weeks. The effective dose in clinical trials has been 90 to 200 mg daily, with research showing the lower end of that range works just as well as the higher dose for reducing both preterm delivery and newborn complications. Progesterone is not effective for preventing PTD in twin pregnancies, and injectable forms of the hormone have not shown the same benefit for women with a short cervix.
Cervical Cerclage
A cerclage is a stitch placed around the cervix to help keep it closed. It’s offered in a few situations: women with a history of second-trimester losses from painless cervical opening typically have one placed between 12 and 14 weeks. Women with a prior preterm birth before 34 weeks whose cervix measures less than 25 mm on ultrasound can have one placed before 24 weeks. In emergencies where the cervix is already dilating without contractions, a rescue cerclage may be placed, again before 24 weeks.
Corticosteroids
If delivery appears likely within the next week, corticosteroids are given to speed up development of the baby’s lungs, brain, and digestive system. The most benefit comes about two days after the first dose, though some protection begins within the first 24 hours. A repeat course can be given if the first round was more than 14 days earlier and delivery still seems imminent.
Magnesium Sulfate
For pregnancies under 32 weeks where delivery could happen within 24 hours, magnesium sulfate is given to protect the baby’s brain. It reduces the risk of cerebral palsy and problems with physical movement after birth.
Health Risks for Preterm Babies
The earlier a baby is born, the more likely complications become. In the first days and weeks, the most common issues involve immature lungs. Respiratory distress syndrome occurs because the lungs haven’t yet produced enough surfactant, the substance that keeps the tiny air sacs from collapsing. Bleeding in the brain (intraventricular hemorrhage), serious intestinal inflammation, blood infections, and vision problems are other early complications, particularly for very and extremely preterm infants.
Hearing loss affects 2% to 10% of preterm babies, compared to 0.1% of the general pediatric population. Preterm infants also carry a higher long-term risk of cardiovascular disease and diabetes.
Long-Term Developmental Effects
Many preterm children catch up developmentally within the first few years, but as a group they face elevated risks for certain challenges. Research has consistently linked preterm birth to higher rates of the inattentive type of ADHD, anxiety, depression, and autism spectrum disorder. Motor coordination problems are also common: one study found that by age 6.5, over 37% of preterm children had developmental coordination disorder, compared to about 5.5% of children born at term.
Language delays, reduced cognitive ability, and executive function difficulties (planning, organizing, and switching between tasks) can show up as poor academic performance once a child reaches school age. Interestingly, assessments done at age 2 are not as reliable at predicting later struggles as those done around age 5, which is why ongoing developmental monitoring through early childhood matters for children born preterm.
These are statistical risks, not certainties. Advances in neonatal care have steadily improved outcomes, and many children born preterm, especially those in the moderate to late preterm range, go on to meet developmental milestones without significant delays.