Premature birth: definition, degrees, causes and risk factors
In brief
Prematurity (preterm birth) is a birth before 37 completed weeks of pregnancy, counted from the first day of the last period; in France, it affects about 7% of births. The outlook depends mainly on how many weeks the baby is born at: it is good in the vast majority of cases after 32 weeks and more guarded before 28 weeks. Regular contractions, leaking fluid or bleeding before 37 weeks mean you should go to the maternity unit straight away.
What counts as a premature birth?
According to the World Health Organization, a birth is premature when it happens before 37 completed weeks of pregnancy (weeks of amenorrhoea). Weeks are counted from the first day of your last period.
According to guidelines from the French College of Gynaecologists and Obstetricians (CNGOF), about 60,000 babies are born prematurely each year in France, or 7.4% of births. Half of these births follow spontaneous labour. The way maternity units are organised in the Paris region (Île-de-France), described on our page Giving birth in Paris, means each woman can be directed to the unit suited to the stage of her pregnancy.
What are the degrees of prematurity?
The baby's outlook depends above all on gestational age at birth. There are three levels.
| Degree | Born at | What it means |
|---|---|---|
| Moderate or late prematurity | 32 to 36 weeks + 6 days | The most common form. The outlook is usually very good; temperature, feeding and breathing are monitored, sometimes in a neonatal unit. |
| Very premature | 28 to 31 weeks + 6 days | Birth is recommended in a maternity unit with neonatal intensive or high-dependency care. |
| Extremely premature | Before 28 weeks | Significant risks (breathing, brain, bowel); birth in a level 3 maternity unit with neonatal intensive care. |
The French national EPIPAGE-2 study, carried out in 2011, measured survival by stage of pregnancy: 98.9% of babies born between 32 and 34 weeks and 93.6% of those born between 27 and 31 weeks survived to discharge from hospital. It was 75.3% at 26 weeks, 59.1% at 25 weeks, 31.2% at 24 weeks and under 1% before 24 weeks.
When a very premature birth is likely, the mother is transferred before the birth (in utero transfer) to a suitable maternity unit: this is safer than transferring the newborn after birth.
What is the difference between spontaneous and medically indicated premature birth?
Spontaneous premature birth
It happens without a medical decision, through labour that starts too early (contractions that change the cervix) or through preterm premature rupture of the membranes ("waters breaking" too early). Spontaneous labour accounts for about half of premature births.
Medically indicated premature birth
The team decides to deliver the baby early, by induction or caesarean section, because continuing the pregnancy would be more dangerous for the mother or the baby. Examples: severe pre-eclampsia, significant growth restriction with signs of foetal distress, placental abruption, or haemorrhage due to placenta praevia. See also bleeding in the second and third trimesters.
What are the main risk factors for premature birth?
Several situations increase the risk. Identifying them means monitoring can be adapted.
Linked to the current pregnancy
- multiple pregnancy (twins, triplets);
- bleeding in the second or third trimester, placenta praevia;
- too much amniotic fluid (polyhydramnios), which stretches the womb;
- infections: kidney infection (pyelonephritis), fever caused by infection, listeriosis, infection of the membranes.
Linked to the womb and cervix
- an abnormally shaped womb, or a large fibroid distorting the cavity;
- a short cervix or cervical insufficiency, a previous cone biopsy;
- exposure in the womb to diethylstilbestrol (DES), in women whose mother took this medicine during pregnancy before it was banned at the end of the 1970s.
Linked to past history and lifestyle
- a previous premature birth or late miscarriage: this is the most important risk factor;
- smoking: stopping is the only preventive measure proven to work in the general population;
- very young or older maternal age, being underweight;
- difficult living conditions, physically demanding work, late or inadequate antenatal care.
In many cases, no risk factor is found. Every pregnant woman should therefore know the warning signs.
Can premature birth be prevented?
The CNGOF guidelines set out which measures help and which do not:
- Stopping smoking: recommended for everyone, with suitable support.
- Measuring the cervix by ultrasound between 16 and 22 weeks in women who have previously given birth before 34 weeks: a cervical stitch (cerclage) may be offered if the cervix is shorter than 25 mm before 24 weeks.
- A planned cervical stitch after at least three late miscarriages or premature births.
- Vaginal progesterone for women expecting one baby, with no previous history, in whom a short cervix is found between 16 and 24 weeks.
- Strict bed rest and prolonged hospital stays are not recommended for threatened premature labour, as they have no proven benefit.
How is threatened premature labour treated?
When premature labour is suspected, the maternity unit assesses the cervix (internal examination, ultrasound) and looks for a cause, especially an infection. Depending on the situation:
- Antenatal steroids: two injections given to the mother, recommended before 34 weeks, to speed up the maturation of the baby's lungs. They reduce newborn deaths and breathing difficulties.
- Magnesium sulphate by drip if birth is imminent before 32 weeks, to protect the baby's brain.
- Tocolysis: medicine that slows contractions for 48 hours, allowing time to give the steroids and arrange a transfer if needed.
- If the waters break early: hospital admission, antibiotics to prevent infection, and monitoring; birth is only brought on if there is infection or as the due date approaches.
What are the signs of premature labour that need urgent care?
Before 37 weeks, the following particularly suggest premature labour is starting: regular contractions (more than a few an hour), even if not very painful; period-like pains or heaviness in the lower abdomen; a leak of fluid; unusual or pinkish discharge.
Some signs should not wait for your next appointment. Go directly to your maternity unit's emergency department (open day and night), at the unit where you are registered (Maternité Sainte-Félicité or Clinique Sainte-Thérèse), if you have:
- any vaginal bleeding, even light;
- a leak of fluid, clear or coloured, from the vagina;
- regular or painful contractions before 37 weeks;
- fewer or no movements from the baby (once you usually feel them);
- a fever of 38 °C or more, shivering, or burning when passing urine with back pain;
- severe headaches, vision problems, pain under the right ribs or in the pit of the stomach, sudden swelling of the face or hands;
- severe or constant abdominal pain, a fall or a blow to the abdomen;
- intense itching of the palms and soles of the feet, especially at night.
If you feel faint, have heavy bleeding or very severe pain, call 15 (SAMU) or 112 in France, or your local emergency number.
Frequently asked questions
From what age can a premature baby survive?
According to the French national EPIPAGE-2 study (2011), survival to discharge from hospital was 31% at 24 weeks, 59% at 25 weeks, 75% at 26 weeks and over 90% between 27 and 31 weeks. At the earliest stages, care is discussed case by case with the parents.
Are evening contractions a sign of premature labour?
A few painless contractions, especially in the evening or after exertion, are common and normal. They become worrying if they are regular, close together, painful or come with a leak of fluid or bleeding: contact the maternity unit.
If my first baby was premature, will the next one be too?
The risk is higher but not certain. Closer monitoring is offered, including an ultrasound measurement of the cervix between 16 and 22 weeks if your first baby was born before 34 weeks.
Do I need bed rest for threatened premature labour?
Strict bed rest is not recommended, as it has shown no benefit. Your team will adjust your activities and time off work to your situation.
References
- Sentilhes L, et al. — Prevention of spontaneous preterm birth: Guidelines for clinical practice from the French College of Gynaecologists and Obstetricians (CNGOF). Eur J Obstet Gynecol Reprod Biol, 2017 — doi:10.1016/j.ejogrb.2016.12.035 — PMID 28068594
- Schmitz T, et al. — [Preterm premature rupture of membranes: CNGOF Guidelines for clinical practice - Short version]. Gynecol Obstet Fertil Senol, 2018 — doi:10.1016/j.gofs.2018.10.016 — PMID 30392986
- Ancel PY, et al. — Survival and morbidity of preterm children born at 22 through 34 weeks' gestation in France in 2011: results of the EPIPAGE-2 cohort study. JAMA Pediatr, 2015 — doi:10.1001/jamapediatrics.2014.3351 — PMID 25621457
Dr Olivier KadochObstetrician-gynaecologist and gynaecological surgeon in Paris (16th and 5th arrondissements). Former chef de clinique-assistant (senior registrar) at the Paris public hospitals (AP-HP); individually accredited by the French National Authority for Health (HAS). RPPS 10003957809. Background and practice locations
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