Twin Pregnancy - Double the Trouble?

Multiple pregnancies demand much closer scrutiny to ensure happy, healthy arrivals, writes obstetrician Dr Emma Parry 

Many a woman, newly pregnant for the first time, has secretly hoped for twins - double the fun with half the effort, right? But, as any mum of twins will tell you, be careful what you wish for. From the first weeks of pregnancy, the stress, the extra load and the number of scans more than doubles.

Fortunately, only one in 75 women finds out she's pregnant with more than one baby (usually twins). Most women find out at the first scan which can be as early as six weeks, or when they go for the nuchal translucency scan which is usually around 12 weeks. In some cases a woman may have very bad morning sickness (hyperemesis gravidarum) and will have a scan to check for multiples because that can cause severe morning sickness.

Twin pregnancies can be a result of the fertilisation of two separate eggs. These are fraternal or non-identical twins and account for two thirds of cases. They have individual placentas and are known as "dichorionic" twins.

For the other third there is one fertilised egg, which splits into two embryos very early in development. These are identical twins and usually share a placenta and are known as "monochorionic" twins.

The perinatal mortality for singletons is around 10 in every 1000 babies, while for twins it's 30 for every 1000 babies. Still, while multiple pregnancy is more complicated at all stages of the pregnancy and delivery, the majority of women and babies do well with careful monitoring and intervention.

Choosing a lead maternity carer
Usually this is one of the first issues to consider once you know you are pregnant. Some women have already chosen their midwife or doctor before they realise they are expecting more than one baby. You may need to reconsider your choice because multiple pregnancy is more complicated.

Government guidelines recommend women with a multiple pregnancy have an obstetrician or a hospital-based obstetric-led service. These are guidelines only, and in certain areas, such as rural parts of New Zealand, the care may be managed in a shared way.

Within multiple pregnancy there are different levels of complexity. For example, if problems develop it may trigger a referral from an obstetrician to  a foetal medicine unit. Problems may include growth problems for one or both babies very early, conditions that arise in monochorionic twins only such as twin-to-twin transfusion syndrome and one or both babies having an abnormality.

Down syndrome screening
Multiple pregnancy does not increase the risk of a particular baby having Down syndrome. Where babies are non-identical, each baby will have his own risk. This means the risk of having a baby with Down syndrome will double - just as buying two lottery tickets doubles your chances of winning the jackpot.

However, when the babies are identical, the risk of having a baby with Down syndrome is about the same as for a singleton as the babies will share the same genetic make-up. If one baby has a genetic abnormality, they almost certainly will both have it.

Pre-term birth
Pre-term birth is what we call birth that occurs between 20 and 37 weeks gestation. In cases of multiple babies, birth often occurs in this time frame.

Pre-term birth may be iatrogenic (planned by health professionals) or spontaneous. In the case of a multiple pregnancy, it is common for women to go into early spontaneous labour.

The main reason for this is thought to be an increased stretch of the uterus muscle. This stretch has an effect on the chemicals at a cellular level which increases the contraction of the muscle. Not a great deal can be done about this, although some research is currently ongoing into ways to reduce this stretch effect.

Another way to reduce the chance of spontaneous pre-term labour is to cut out or reduce smoking. Of course, this is pretty standard healthcare advice, with many other benefits for both Mum and baby. Even quitting smoking halfway through a pregnancy is better than not at all. Smoking can also have very negative effects on the growth of the baby.

Women pregnant with twins are often told they should have plenty of rest and put their feet up. This is true to a degree, but studies of women pregnant with twins who were recommended bed rest had surprising results - the women on bed rest actually had a higher rate of pre-term birth than those treated in the usual way. We no longer recommend bed rest for these mums.

However, a diet high in fish oils has been shown to help reduce spontaneous pre-term labour. Unfortunately you need an awful lot and, on a New Zealand diet, probably the only way to get it is with fish oil capsules.

Women who have had previous surgery on their cervix are at a higher risk of spontaneous pre-term labour, although the level depends on factors associated with the surgery. A previous termination of pregnancy also increases the risk of spontaneous pre-term labour. This means it is important to tell your LMC about any previous surgery.

A planned pre-term birth is often due to complications such as pre-eclampsia, diabetes and poor growth. The midwives and doctors caring for women with these conditions will try to get the pregnancy as far along as possible before delivery. This may mean a boring spell in hospital, but it's worth it. The uterus is the best incubator for babies and the longer they stay in the better, if both Mum and babies are stable.

Sometimes it can be hard to tell if labour has started early. Pre-term rupture of the membranes (your waters breaking) is not always obvious, as at very early gestations there may not be much fluid. Regular, painful contractions are concerning. However, some women may have a change in discharge and a heavy feeling as their only signs. Any sign is important and should prompt a phone call to the LMC.

If there is a suspicion that a woman is in spontaneous pre-term labour a number of tests can be done to help work out the chances of this progressing. In many cases it turns out to be a "false labour".

If a pre-term birth is expected the obstetrician will usually prescribe a course of steroids - two injections. These have been shown to reduce complications for babies after birth. We should be very proud as this was a New Zealand discovery by Sir Graham Liggins. The discovery has saved the lives of thousands of babies around the world.

Growth problems
Multiple pregnancies are more likely to lead to growth problems (intra-uterine growth restriction or IUGR) than singletons. It is thought that this is in part due to the requirement for a larger part of the surface of the uterus to form the placenta. As the pregnancy progresses, the placenta/s is bigger than a singleton's, and this may result in a less well established placenta.

There is overcrowding! In addition, the way the placenta implants can be less than ideal which results in growth problems and can also lead to pre-eclampsia.

When there is sub-optimal placental size and function, the babies will adapt. But as it's an environment of reduced nutrition, there will often be a reduction in growth of the babies.

In multiple pregnancy the method of measuring the Symphysio-Fundal Height, by measuring with a tape measure on the mother's abdomen, is prone to more errors, and, as previously mentioned, there is a higher chance of growth problems, so a regular ultrasound scan is used instead to monitor the babies' growth.

During the scan the sonographer will measure the head, abdomen and thigh bone. These will be used to calculate an estimated foetal weight. This can vary by 10-15% either way, which is quite a big margin of error! In addition, the activity of the babies and the fluid around them will be assessed as another way to check the babies' wellbeing.

When a baby has restricted nutrition from the placental blood flow it will adapt. It is like an adult not eating enough food - the baby has essential organs which will always get priority. These include the brain, heart muscle and the adrenal glands which produce adrenalin. Other areas will miss out, such as the kidneys which make urine, forming most of the liquid around the baby. So, when there is reduced nutrition, reduced fluid may be a sign of the baby adapting to this. Also, the baby will move less and grow less as these both burn up calories.

This situation is greatly concerning which is why careful monitoring via ultrasound is so important.

In non-identical twins monthly scans will usually start around 24 weeks gestation. These twins are at lower risk of problems than identical twins. In identical twins, the New Zealand Maternal Fetal Medicine Network (NZMFMN) recommends that two-weekly scans start at 16 weeks. This seems very early, but is important to detect other problems which only identical twins have in addition to growth problems such as twin-to-twin transfusion syndrome (TTTS). This condition accounts for most cases of increased perinatal mortality which monochorionic twins have. The treatment is keyhole surgery which can be performed only in Auckland. It is important to identify it early.

So if there are growth problems, what happens? In non-identical twins this often occurs well after the time they become viable (able to survive outside the womb). It usually requires more scans and closer monitoring. Usually one is the troublemaker (because he's smaller) and the other is growing well.

However, usually the troublemaker needs to be born at some stage, because of concerns that show up on the ultrasound scan early.

This means that the well-grown twin also has to be born early even if he is fine. It is quite curious, as after birth in the neonatal unit, the smaller twin often does better! He seems to be hungry and catches up quickly while the bigger twin gets a shock at being brought out early.

In identical twins growth problems are more likely to become an issue around the time of viability (22 to 28 weeks).

At this point the pregnancy becomes very high risk and requires increased scans and surveillance.

There can be some very difficult decisions for the parents around how much intervention to take. For instance, allowing the babies to die if they are too small to survive or having a termination of one to give the other a chance when the smaller one has no hope of survival.

Bleeding and other problems
In addition to the problems above, due to the larger placenta/s in twin pregnancies, there is a higher chance of bleeding in pregnancy. This can be from the edge of the placenta or due to the placenta being previa. This means the placenta is in front of the babies over the cervix. If this is the case at the time of delivery, a Caesarean section will be required.

Pretty much any pregnancy complication will be increased when there is a multiple.

The birth
Mums with twins will feel very uncomfortable towards the end of pregnancy. The time of delivery is usually earlier than for a singleton. In the case of identical twins it seems it is safe to wait until 36-37 weeks gestation to deliver the twins. If they're non-identical it is safe to wait to 37 weeks. Most triplets are delivered at 34 weeks gestation.

There are no good studies on the best mode of delivery. In general, if there are no concerns with a twin pregnancy and the first baby is lying head first, then a vaginal delivery is a good idea. This allows the babies to be exposed to contractions which kick-start the lungs. However, most twins are born by C-section.

In New Zealand units there will be a senior doctor on hand for a twin vaginal delivery. There will usually be paediatricians or paediatric nurses available and sometimes an anaesthetist. It can feel quite busy, but often team members wait outside the delivery room until they are needed.

So once the babies are born the real excitement begins! The attention now turns to making sure the mother has the help she needs around breastfeeding, sleep and caring for her double (or triple) delights. 

Dr Emma Parry is a Specialist Obstetrician and Gynaecologist and a sub-specialist in Maternal-Fetal Medicine. She is a spokesperson for the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG). 

For more help
Dr Emma Parry is the medical adviser to the Multiple Birth Association, a nationwide consumer support group with clubs in most major centres. The MBA has a separate triplet support group with social networking sites, go to multiples.org.nz.
For more on foetal medicine services in New Zealand have a look at the New Zealand Maternal Fetal Medicine Network .
If a woman has problems finding a lead maternity carer, the local hospital must provide care. Phone the Ministry of Health: 0800 MUM 2 BE (0800 686 223).