Full term for pregnancy is defined as 37 – 42 weeks from the beginning of the last menstrual period. Premature birth is a very important condition, being the leading cause of death and disability of babies.

Despite many advances in obstetric and neonatal care, premature birth still occurs in approximately 10% of pregnancies and significantly premature babies are far more likely to die or become disabled than babies born at full term.

A number of babies are born prematurely because of medical intervention to bring about their birth. This usually occurs when either:

  1. The mother’s wellbeing is threatened by continuation of the pregnancy (for example she may suffer from severe preeclampsia or a serious heart problem) or
  2. The risks of staying inside the womb are greater for the baby than those of being born. This usually occurs if the placenta (afterbirth) is not functioning well and the baby is growing very poorly and showing signs of becoming short of oxygen.

However the majority of premature births occur because the mother simply goes into Premature – or Preterm – Labour (PTL).

While we classify premature births as all deliveries between 20 and 37 weeks, the implications of premature birth vary greatly according to gestation. Babies born at close to 37 weeks have outcomes similar to – or even better than – babies born at full term yet babies born below 25 weeks almost invariably die, and those born between 25 and 29 weeks are at high risk of dying and face significant risks of handicap if they survive.

So who is at risk of going into premature labour (PTL)?

  1. Women who have had premature labour in a previous pregnancy, even if the cause of the previous PTL was not apparent.
  2. Women with a weak cervix (so called “cervical incompetence”), which can be due to previous operations involving the cervix
  3. Women with twins, triplets or more
  4. Women who have achieved pregnancy through Assisted Reproductive Technology (ART) – usually IVF.
  5. Women with abnormalities of the womb, including:
    • Fibroids
    • A bicornuate uterus
    • An arcuate or subseptate uterus
  6. Women who have had recurrent vaginal bleeding after approximately 15 weeks gestation
  7. Women who have had a placental abruption (part of the placenta having lifted away from the wall of the womb, causing pain and bleeding
  8. Women who have sustained an injury to their abdomen
  9. Women with some infections, including:
    • Urinary Tract Infections (UTIs)
    • Some vaginal infections, such as bacterial vaginosis
    • Listeriosis

However, a number of women who labour early have no recognisable risk factors for PTL. Similarly the cause of an episode of premature labour may never be apparent.

When can PTL occur?

By definition we call delivering a baby at less than 20 weeks a miscarriage (so contractions and / or bleeding occurring at less than 20 weeks is a threatenedmiscarriage). The 20-week cut off is completely arbitrary and the causes of a late miscarriage are almost always the same as those of early PTL. Premature labour and delivery can occur at any stage between 20 weeks and 37 weeks of pregnancy. Fortunately premature delivery in the 20 – 30 week period is rare.

It is important not to dismiss symptoms at relatively early stages of your pregnancy just because it is “too soon for the baby to come”.

What are the symptoms of PTL?

The symptoms of PTL are essentially those of labour at full term – namely regular,painful contractions or tightening of the womb. In general contractions that are occurring regularly every 10 minutes, are painful (i.e. they make you “breathe” through them) and have been present for more than 30 minutes represent labour until proven otherwise. Vaginal bleeding, loss of a mucous “show” or the waters breaking are also signs of labour.

Sometimes, however, the symptoms of PTL can be less obvious than labour at full term. Rather than having obvious contractions, women can sometimes have low abdominal or back discomfort (”heaviness”) without obvious pains or contractions. Sometimes constant abdominal pain can occur prior to a premature birth. Even small amounts of fluid loss – blood, water or even an increased discharge – can be of some significance. This is why I strongly recommend that you contact me even if you have very mild symptoms that might be PTL, even if we subsequently find that you are not in labour.

Women who have any of the risk factors above should be particularly vigilant about possible symptoms of PTL.

Some conditions can mimic PTL. These include:

  1. A Urinary Tract Infection, or UTI
  2. Constipation
  3. Braxton Hicks (”practice”) contractions
  4. Pain from a fibroid or an ovarian cyst
  5. The pain of ligaments of the uterus being stretched
  6. Muscular or joint discomfort.

However, as mentioned above, it is not safe to assume that your symptoms are not of concern – it is important for you to be checked if anything untoward is occurring.

Is it possible to prevent PTL and Premature Birth?

One of the many disappointments of modern obstetrics has been our inability to prevent premature births. Indeed the number of babies requiring neonatal intensive care is increasing, although this increase is due to:

  • The fact that Neonatal Intensive Care is now offered to babies that would have been allowed to die in the past, e.g. babies born at 24 weeks.
  • The increasing numbers of multiple pregnancies these days. The reasons for this increase are the increased availability of Assisted Reproductive Technologies (ARTs) and the fact that older mothers are more likely to spontaneously conceive twins or triplets.

There are very few interventions that will actually prevent or stop a premature birth. There are no tablets or medications currently available that are proven to prevent premature birth, although recent studies have begun to examine two possibilities:

  • Some studies (not all) have suggested that certain antibiotics might help to prevent premature birth in women with an – otherwise harmless – infection in the vagina called Bacterial Vaginosis (BV).
  • The hormone progesterone is a current focus of research as some early studies have suggested it might help prevent premature labour in women at risk of giving birth early.

Placing a strong stitch around the neck of the womb (cervix) has been shown to prevent premature birth in women who have a weak cervix. These sutures are usually inserted before or early on in pregnancy.

In all other respects our care is focussed on trying to predict premature birth in women at risk (ultrasound scans of the cervix are probably the best method), ensuring premature babies are born in the right place and in optimal condition.

How do we manage PTL?

This largely depends upon the gestation at which you have gone into labour and whether your baby is (or babies are) in good condition or not. It is also important that we consider possible causes of PTL because your baby may have decided to come for a very good reason (infection inside the womb is a good example) and may well be better off being born than remaining inside you.

If you are in spontaneous labour at 35 weeks and your baby is coming head first and is in good condition, we will simply watch you both closely and wait for the baby to deliver normally. If your baby is in the breech (bottom first) or showing signs of being distressed, we might recommend birth by caesarean section.

Equally, PTL can “fizzle out” of its own accord and your pregnancy can continue to a later stage.

Below approximately 32 – 33 weeks we sometimes try to slow premature labour down and gain time before the birth. This is of more benefit to babies at what we call borderline gestations – like 24 to 26 weeks – when staying inside you even for a few days can make a significant difference to your baby’s (babies’) chances of survival and risk of handicap. We also try to hold up premature births in order to give steroid injections to the mother. These steroids (we use betamethasone, also known as Celestone) are the sort of steroids doctors use for severe arthritis and asthma – not the sort of steroids Ben Johnson and Arnold Swazenegger use to build up their muscles! There is very good scientific evidence proving that giving steroids prior to the birth improves a number of outcomes for premature babies, including:

  • Improving their survival chances overall
  • Reducing their need for mechanical respiratory ventilation and long term oxygen
  • Reducing their risk of their fragile blood vessels bleeding into their brain, and
  • Reducing the risk of bowel problems.

There are two main types of medicines we use to slow premature births. One is a blood pressure tablet called nifedipine and the other is an asthma medication called salbutamol. They are both safe in pregnancy and both have the beneficial side effect of reducing contractions of the womb. In general, however, if your premature labour is the real thing, the medications will only slow the birth process down for a couple of days or so – if the baby really is to be born early it will come regardless of whatever we do.

Some women have their waters break at a premature gestation without them going into labour straight away. When this happens we give antibiotics to try to prevent infection and to prolong the pregnancy for as long as possible.

If I get the chance I organise an ultrasound scan when a woman is admitted to hospital in PTL. This gives me important information about:

  • The weight of the baby / babies,
  • The state of the cervix – whether it is dilated (open) or tightly closed,
  • The amount of fluid around the baby / babies (this can help if we are unsure whether the waters have broken or not),
  • The position of the placenta (afterbirth),
  • Which way around the babies are – head first, bottom first (breech) or sideways (transverse), and
  • The wellbeing of the babies – how healthy they are.

I always recommend continuous monitoring of the babies heart rates during the active (strong contraction) part of premature labour. This is to ensure the baby is coping with the contractions.

Whenever I am contemplating a premature delivery (for example, if Mum has preeclampsia) or one of my patients is in PTL, I seek the input of a Neonatal Intensive Care Specialist. NICU specialists are paediatricians who have sub specialised in the intensive care of very premature babies. I often seek the advice of the NICU specialist and introduce them to the parents before a premature baby is (or babies are) born. This ensures that the parents have their questions answered and the parent, myself, and the NICU specialist discuss the plans for the birth and care of the baby(ies) after the birth.

Women who are at increased risk of a premature birth might wish to meet a NICU specialist relatively early in the pregnancy. I am happy to arrange this.

What types of pain relief is available for PTL and premature births?

The short answer to this question is that all of the things we use for pain relief for birth at term (gas, pethidine and epidurals) can be used for premature births. I am perhaps slightly more likely to recommend an epidural for a premature birth than a term labour because:

  • The epidural prevents you from pushing before the cervix is fully open (dilated), and
  • Because there may be an increased chance of an emergency caesarean for a premature birth and caesareans are safest when done under epidural or spinal anaesthetic.

How are premature babies born?

In this day and age premature babies – particularly those below 32 weeks – are more likely to be born by caesarean than normally. This is not because natural labour is inherently more dangerous for a premature baby than one born at full term – it is not. Indeed a great many premature babies are born both normally and in very good condition.

The reason for the great number of caesarean births really relates to the problems that have caused (e.g. preeclampsia or placental abruption) or are associated with (e.g. multiple pregnancy or breech position) the premature birth. It is also very difficult to induce labour at premature gestations so when we intervene to bring about a premature birth we most commonly do so by caesarean.

Where should premature babies be born?

Babies born before 32 – 34 weeks have the best survival chances if they are born in a hospital that has a tertiary, or Level 3, Neonatal Intensive Care Unit (NICU). The Royal Hospital for Women is such a hospital. However, there are only a limited number of Level 3 NICU cots in New South Wales, and 6 of these are at the Royal. Occasionally – and distressingly – we have to move a woman in PTL to another hospital because all of our Level 3 cots are full. This decision is made with your baby’s best interests at heart, although I recognise it can be distressing. Other hospitals nearby that have Level 3 NICUs include Royal Prince Alfred and Royal North Shore Hospitals

What are normal birth weights for premature babies?

The approximate average birth weights for premature babies, by week, are as follows:

Boys Girls
Week1 23 600 570 grams
24 700 650
25 800 750
26 900 870
27 1030 970
28 1200 1100
29 1300 1230
30 1500 1420
31 1690 1600
32 1880 1790

Do remember that in prematurity – as in everything – girls more than make up for smallness with toughness!

What are the outcomes for premature babies?

    For babies that are admitted to a NICU (remembering that, sadly, some babies die before they are born or very shortly after birth), approximate survival figures are:

    • 23 weeks 30%
    • 24 – 25 weeks 50 – 60%
    • 26 – 28 weeks 80 – 90%
    • 29 weeks or more 95% or more


The major short-term complications of prematurity are:

  • Immature lungs requiring mechanical ventilation
  • Patent Ductus Arteriosus (PDA). This is when a blood vessel designed to divert blood away from the baby’s lungs during pregnancy fails to close after the birth.
  • Necrotising Enterocolitis (NEC). An infection / inflammation of the immature gut.
  • Significant sepsis, or infection. This includes meningitis, pneumonia and other serious infections.
  • Intraventricular Haemorrhage (IVH) Grades 3 and 4. This is significant bleeding into the brain.

Typical rates (all expressed as percentages) of short-term complications in New South Wales are:

Week 23 24 25 26 27 28 29 30 31
Ventilation 100 100 100 99 99 95 90 75 65
PDA > 70 70 70 45 45 40 25 15 10 5
NEC > 20 20 20 5 5 5 5 5 3 2
Sepsis > 60 60 60 50 40 40 25 20 10 5
IVH 30 15 15 10 10 5 5 1 1


The main longer-term complications of prematurity and neonatal intensive care are:

  • Retinopathy of Prematurity (ROP) Grades 3 and 4. This is visual impairment resulting from the administration of oxygen to premature babies (this is the cause of Stevie Wonder’s blindness).
  • Chronic Lung Disease (CLD). This is a longer-term lung problem that results from the effects of mechanical ventilation of the lungs. Some babies affected by CLD require long-term oxygen (O2) treatment at home after they have been discharged from hospital.
  • Moderate to Severe Disabilities including Cerebral Palsy (CP), Epilepsy, Learning and Behavioural problems.

Typical rates of these longer – term problems (again as percentages) are:

Week 23 24 25 26 27 28 29 30 31
ROP 75 30 20 15 5 1 1 0 0
CLD 40 45 40 40 35 20 15 5 5
02 20 20 20 20 15 5 5 <3 <1
MSD 55 35 20

* = Moderate to Severe Disability.

Remember that these are overall figures. Babies born in good condition and who have been exposed to the steroid injections might do a little better than these averages. On the other hand babies who have suffered poor growth in the womb (so are smaller than their “peers”) or are born in poor condition may do worse.

You can see that babies born at very low gestations – 23 to 25 weeks – not only have very relatively low chances of survival but high chances of complications and long term problems. On the other hand outcomes (both in terms of survival and risk of handicap) for babies born between 26 and 29 weeks have improved considerably over recent years such that these babies have good chances of survival and relatively low risks of significant ongoing problems. Remarkably, by 31 weeks survival and the risk of long-term problems have become very close to figures for term babies. This is why beyond 30 weeks or so our focus often shifts from trying to prevent a premature birth to ensuring that the premature baby is born in the best condition possible.

Who decides if my extremely premature baby should be resuscitated?

The decision whether or not to resuscitate very premature (less than 26 weeks) newborns is emotive and contentious. Many parents – for obvious reasons – wish the doctors to “pull out all the stops” and do as much as possible to save a baby, even if it is extremely premature. Other parents – equally understandably – feel that they don’t wish to see their very premature baby suffer Neonatal Intensive Care when the chances of survival are slim at best and the risk of permanent handicap is high.

At the end of the day this decision is the parents and our aim is to give them as much information as possible. In general, however, our advice would be:

  • At below 24 weeks the outlook for the baby is likely to be very poor and if the baby survives the chances of considerable handicap are high. We would tend to discourage active resuscitation for a baby born below 24 weeks.
  • At 26 weeks or more we would generally encourage parents to choose to have their baby resuscitated as long as it is of normal weight and in good condition at birth. As you can see from the figures above, the chances of the baby surviving with minimal problems is reasonable (and remember even at full term there is a very small risk of death or disability for babies).
  • Between 24 and 26 weeks we should individualise based on factors such as birth weight, condition at birth, attendant problems and – most importantly – the parents’ wishes.

Just occasionally we can be wrong about a baby’s gestation or it can be born much bigger and in better condition than we expected (although unfortunately the reverse is always true) so I like to have a NICU specialist attend for all very premature births so that if necessary we can change our management plans based on new information.

Dr Rob Buist

Sources / Acknowledgments:

  • The birthweight data comes from New South Wales charts published in 1996 by Beeby, Bhuta and Taylor.
  • The rates of survival and complications come from the following publication:
  • Preterm Outcome Table (POT) – A Simple Tool to Aid Counselling Parents of Very Preterm Infants. Authors Srinivas Bolisetty, Barbara Bajuk, Abdel-Latif Me, Lee Sutton and Kei Lui. This article has been submitted to a medical journal for publication. I have reproduced material from it with the exceptionally kind permission of the authors.