If you have passed your due date, it may seem like your pregnancy is never going to end and you may become increasingly anxious about labour and your baby’s wellbeing. This is particularly so if you are very tired, uncomfortable and feel heavy and ungainly. Try to relax, the end is in sight.
If you go past your estimated date of delivery (EDD) your midwife and obstetrician will keep a close check on you and your baby. Post-maturity can result in some complications and most obstetricians and midwives advise that your baby should be delivered no later than 42 weeks.
Why are some babies overdue?
Approximately 85% of babies are born after their due date. This can be due to a number of factors including getting the date of conception wrong. The date of conception is often difficult to pinpoint exactly, even if you have a regular 28 day cycle. This means that the EDD will also be hard to calculate.
You are more likely to have a post-term pregnancy if previous pregnancies went beyond 40 weeks.
Are overdue babies at risk of complications?
The great majority of babies are born healthy whether they arrive at term or later. However, the risk of complications and a difficult birth rises for babies born after 42 weeks.
If your pregnancy has gone beyond term you will be carefully monitored for signs of possible placental deterioration. The job of the placenta is to supply your baby with enough nutrients and oxygen for his needs. In the later weeks of pregnancy, however, changes in the placenta (calcium deposits on the walls of the small blood vessels and protein deposits on the placental surface) can limit blood flow through the placenta, making it progressively inefficient. Occasionally, the placenta fails to nourish and support the baby adequately - placental insufficiency. If this happens you will be advised to have your labour induced.
The effect of uterine contractions on an unhealthy placenta may cause foetal distress. A post-term baby is more likely to pass meconium (the first stool) during labour so the risk of meconium aspiration and breathing problems or infection is increased.
A post-mature baby may be bigger than average, which can result in a longer labour due to inefficient uterine action or cephalopelvic disproportion (baby’s head is too big to pass through the pelvis). If this is suspected an elective caesarean section is advised.
If your baby is post-term and larger than average, there may be difficulties at delivery and forceps or vacuum delivery can be necessary. There is also an increased risk of difficulty in delivering the shoulders (shoulder dystocia). For the mother, there is a higher risk of trauma to the perineum (including the vagina, labia and rectum). There is also a higher risk of caesarean section with its associated complications including bleeding and infection.
Post-maturity is also a risk. A post-mature baby may have lost fat from all over his body and the skin may appear dry and wrinkled. The skin may even have begun to peel, particularly on the hands and feet. This dryness and peeling quickly resolves after birth. Massaging the skin with oil really helps.
Will I be induced?
If you are overdue there are a number of different ways of monitoring your baby’s wellbeing. If any of the tests indicate that it is no longer safe for the baby to remain in the uterus labour may be induced.
Foetal movement recording
The most reassuring sign that all is well with your baby is regular movements. As you are the best judge of whether your baby is moving normally, you will be asked to keep a kick-chart to record baby’s activity. If there are less than 10 movements in 12 hours contact your midwife or obstetrician. A reduction in the number of movements may be a sign of deteriorating placental function.
Electronic foetal monitoring
Electronic foetal monitoring using a cardiotocograph (CTG) may be done to check your baby’s heartbeat. It is usually done over a 30-minute period. If the heart rate is satisfactory it is unlikely that you will have your labour induced. However, you may be offered an ultrasound scan for extra reassurance.
An ultrasound scan may be done to assess the amount of amniotic fluid surrounding your baby. If the placenta has begun to deteriorate the amount of amniotic fluid may be decreased, in which case you will be advised to have your labour induced.
A biophysical profile may include electronic foetal monitoring and a foetal ultrasound to measure your baby’s heart rate, muscle tone, movement, breathing and the amount of amniotic fluid around your baby.
Doppler flow study
This is a type of ultrasound scan that measures the blood flow through the placenta.
Dr Bridget Maher, MB, BCh, BAO NUI
First Published 10th August 2007
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