Hearing the words preterm birth can make time feel strangely elastic: everything speeds up—appointments, monitoring, decisions—while your mind tries to catch up. Is the baby safe? Is it “real” labor? What happens next? A preterm birth simply means birth before 37 completed weeks of pregnancy, but behind that definition sits a spectrum of situations, from a short hospital check to weeks of neonatal care.

A few days can matter (lungs, brain, digestion, temperature control, immune defenses). And yet many families are surprised by how structured the medical approach is: clinicians assess the cervix, the contractions, the membranes, infection markers, and fetal wellbeing, then choose interventions that either buy time or plan a safer delivery.

What “preterm” means (and why a single day counts)

A preterm birth occurs before 37+0 weeks. Medicine counts completed weeks, so 36+6 is still preterm.

What matures late in pregnancy?

Look after your family’s health

Download Heloa

Use your phone’s camera to scan the QR code and download Heloa

Veillez sur la santé de votre famille

Try Heloa

Lungs (surfactant improves breathing after birth)
Brain (rapid growth and wiring)
Gut (feeding tolerance)
Skin and fat stores (heat conservation)
Immune function (higher infection susceptibility)

You may also hear “premature.” In everyday language it often means the same thing as preterm birth, though clinicians prefer “preterm” for accuracy.

Preterm birth, low birth weight, and SGA: not the same diagnosis

Preterm birth = when the baby is born.
Low birth weight = how much the baby weighs (often <2,500 g), at term or preterm.
Small for gestational age (SGA) = weight lower than expected for the number of weeks (often <10th percentile).

A baby can have preterm birth without being SGA, or be SGA at term.

How pregnancy dating works (and why due dates sometimes shift)

Gestational age is traditionally counted from the first day of the last menstrual period (LMP), but cycles vary and ovulation isn’t clockwork. A first-trimester ultrasound (before 14 weeks) is the most accurate tool: dating by crown–rump length is usually accurate within 5–7 days. If LMP and ultrasound differ by more than about a week, clinicians generally follow the ultrasound date.

Gestational age categories: one term, several realities

Clinicians classify preterm birth like this:

Extremely preterm: <28 weeks
Very preterm: 28 to <32 weeks
Moderate preterm: 32 to <34 weeks
Late preterm: 34 to <37 weeks

Late preterm births are the most frequent. Extremely and very preterm births are less common, but usually require NICU care.

Threatened preterm labor: why it feels blurry

“Threatened preterm labor” is used when birth might occur early because there are:

regular, persistent uterine contractions, and/or
signs the cervix is changing (shortening, thinning/effacing, opening).

Many people have contractions that are uncomfortable yet not “true” labor. Dehydration, fatigue, or a urinary tract infection (UTI) can irritate the uterus. The key question: is the cervix changing?

Different pathways to preterm birth

Spontaneous preterm birth

Labor starts on its own (contractions with cervical change) or after early rupture of membranes.

Medically indicated (iatrogenic) preterm delivery

Sometimes early delivery is safer: severe preeclampsia, fetal distress, significant fetal growth restriction, or major placental complications.

PPROM: water breaking before 37 weeks

PPROM (preterm prelabor rupture of membranes) increases concern for infection, umbilical cord complications, and decisions about whether to prolong pregnancy or deliver.

How common is preterm birth?

Globally, preterm birth affects about 1 in 10 births. Most are late preterm. For families, it can mean sudden hospitalization, pumping schedules, siblings to organize, and long hours in a neonatal unit.

Why preterm birth can happen: a multifactorial picture

Clinicians often think in overlapping routes:

infection/inflammation
cervical factors
placental disease
maternal medical conditions
fetal compromise
multiple pregnancy

Infection and inflammation

Inflammatory messengers (cytokines and prostaglandins) can trigger contractions, weaken membranes, and promote cervical change. Contributors include UTIs, bacterial vaginosis, and intra-amniotic infection (chorioamnionitis).

Cervical insufficiency and short cervix

A short cervical length (often ≤25 mm) in mid-pregnancy is linked to higher risk of spontaneous preterm birth in singleton pregnancies. Depending on history and gestational age, options may include progesterone or, in selected cases, a cerclage.

Placental and membrane problems

Examples:

placenta previa (bleeding)
placental abruption (early separation, can be urgent)
placental insufficiency (reduced oxygen/nutrient transfer)

Ruptured membranes raise infection risk, infection can weaken membranes.

Hypertension, preeclampsia, and growth restriction

With preeclampsia, maternal organs and placental function can deteriorate. Fetal growth restriction often reflects placental underperformance and may prompt close ultrasound monitoring (growth, amniotic fluid, Dopplers).

Modifiable factors (without blame)

Smoking, alcohol or non-prescribed drugs, dehydration, severe fatigue, chronic stress plus barriers to care, and short interpregnancy intervals can contribute—without explaining every preterm birth.

Signs of preterm labor: when to call

Call promptly if you are under 37 weeks and have:

4 or more contractions in an hour, especially if regular
pelvic pressure, constant low back pain, period-like cramps
watery/bloody/mucus-like discharge, or much more discharge

Seek urgent evaluation for:

a gush or continuous trickle of fluid
any vaginal bleeding
clearly decreased fetal movement

While calling: time contractions, note fever or pain, drink water, rest on your side. Strict bed rest hasn’t shown benefit and can increase clot risk.

Hospital evaluation: how risk is assessed

Typical triage includes:

vital signs, symptom history
fetal heart rate monitoring (cardiotocography)
cervical assessment when appropriate

Cervical length ultrasound and targeted tests

A transvaginal ultrasound measures cervical length, ≤25 mm is a common “short cervix” threshold. Some units use fetal fibronectin (fFN): a negative test is reassuring for low short-term birth risk, a positive test needs clinical context.

Infection checks and baby assessment

Urine tests, swabs, blood tests, and ultrasound (growth, fluid, sometimes Dopplers) may be used.

When preterm birth seems likely: treatments and decisions

The goal is often to gain 24–48 hours safely for key treatments or transfer.

Tocolysis (tocolytics) may briefly delay contractions in selected cases, often before 34 weeks.
Antenatal corticosteroids (commonly 24–34 weeks when delivery within 7 days is likely) support lung maturation.
Magnesium sulfate may be offered for fetal neuroprotection when birth before 32 weeks is expected.
Antibiotics are used for suspected infection, often for PPROM, and sometimes during labor for Group B Strep prevention.

Early delivery may be safest with severe preeclampsia, major bleeding, suspected intra-amniotic infection, fetal distress, or severe growth restriction.

If advanced neonatal support is needed, in-utero transfer is prioritized when safe.

What happens right after a preterm birth?

Breathing, warmth, feeding

Depending on gestational age, a preterm baby may need CPAP, surfactant, or ventilation. Warming starts immediately, skin-to-skin (kangaroo care) is encouraged as soon as safe. Feeding often prioritizes human milk, sometimes via tube feeding, very preterm infants may need milk fortification.

Infection prevention and developmental care

NICUs emphasize hand hygiene, careful monitoring, and comfort-focused care (sleep protection, gentle positioning, pain relief).

Parents’ place in care

When safe, parents often participate in diapering, comforting, feeding, and skin-to-skin—actions that support stability and bonding.

Short-term complications linked to prematurity

Risks vary by gestational age, but may include:

respiratory distress syndrome (RDS) and apnea of prematurity
intraventricular hemorrhage (IVH)
necrotizing enterocolitis (NEC)
retinopathy of prematurity (ROP)
infections and jaundice

Long-term outcomes and follow-up

Many children born after preterm birth do very well, especially with structured follow-up.

Corrected age (adjusting for weeks early) guides milestone expectations.
Developmental follow-up may flag motor, attention, or learning differences early, allowing timely support.
Some very preterm infants develop bronchopulmonary dysplasia (BPD).
Vision and hearing screening are standard before and after discharge.

Myths that add stress

“I caused it.” Preterm birth is often multifactorial, a risk factor is not proof of fault.
“Bed rest fixes it.” Strict bed rest hasn’t prevented preterm birth and can add harms.
“Stress is the only cause.” Stress can interact with other factors, support is worth asking for.

Key takeaways

Preterm birth means birth before 37 completed weeks, timing affects organ maturity.
Threatened preterm labor involves persistent contractions and/or cervical change—persistent symptoms deserve assessment.
Pathways to preterm birth include infection/inflammation, PPROM, placental disease, hypertension/preeclampsia, growth restriction, multiple pregnancy, and cervical factors.
Warning signs (regular contractions, pressure, bleeding, leaking fluid, decreased movements) warrant a prompt call or urgent evaluation.
Hospital care uses monitoring, cervical assessment (including length), and targeted tests (such as fFN) to guide decisions.
If preterm birth seems likely, care may aim to gain 24–48 hours for steroids, magnesium sulfate when appropriate, antibiotics when indicated, and transfer if needed.
After birth, priorities are breathing, warmth, feeding (human milk), infection prevention, and developmental care—with parents actively involved.
Professionals and resources can support you, you can also download the Heloa app for personalized guidance and free child health questionnaires.

Questions Parents Ask

Can preterm labor stop on its own—and can I go home afterward?

Yes. Many episodes of suspected preterm labor settle, especially when the cervix stays stable and tests suggest a low short‑term risk of delivery. If your symptoms improve and monitoring is reassuring, your team may suggest going home with clear return precautions. You can ask what signs to watch for (contractions pattern, fluid leakage, bleeding, fever, reduced movements) and whether any follow‑up is planned, such as a repeat cervical length check.

How long do preterm babies usually stay in the NICU?

It depends mostly on gestational age and how smoothly feeding, breathing, and temperature control develop. A common rule of thumb is “until close to the due date,” but many babies go home earlier, and some need longer. Discharge is usually based on milestones—stable breathing, maintaining body temperature, gaining weight with feeds (breast, bottle, or tube as needed), and being medically steady—rather than a specific number on the calendar.

Will a baby born preterm “catch up” in development?

Many do, and progress can be very encouraging. Clinicians often use corrected age (adjusted for weeks early) when looking at milestones in the first 2 years. Some children may need extra support (physio, speech, developmental follow‑up), and that’s not a failure—just a way to give your child the best start, at their own pace.

Preterm birth: what parents need to know when a baby may arrive early