A multiple pregnancy may be the result of the fertilisation of a single egg that then splits to create identical foetuses, or it may be the result of the fertilisation of multiple eggs that create fraternal foetuses, or it may be the combination of the two.
In humans, the average length of pregnancy is 38 weeks, with a single foetus. This average decreases for each additional foetus: to thirty-six weeks for twin births, thirty-two weeks for triplets, and thirty weeks for quadruplets. With the decreasing gestation period, the risks from immaturity at birth and subsequent viability increase with the size of the sibling group.
If the mother takes fertility drugs or has in vitro fertilisation to help her get pregnant, chances of multiple pregnancy increases. Fertility drugs help the body make several eggs at a time. This increases the chance that more than one of the eggs will be fertilised.
When in vitro fertilisation is used the doctor may put several fertilised eggs in the uterus to increase the chances of having at least one baby. This makes a multiple pregnancy more likely.
Identical triplets come from a monozygotic pregnancy, three foetuses from one egg. Triplets are far less common than twins.
Quadruplets are much rarer than twins or triplets. Many sets of quadruplets contain a mixture of identical and fraternal siblings, such as three identical and one fraternal, or two pairs of identical twins.
While the mother may feel that she is carrying more than one baby, only the doctor can say for sure. A foetal ultrasound will be done to confirm this. This test will give the doctor a clear picture of how many babies are in the mother’s uterus.
If the tests show that the mother is carrying multiples, more ultrasounds will be done and the doctor will use these tests to check for any signs of problems the mother or her babies may have as they grow.
A multiple pregnancy term requires additional precaution and care. The mother should always be conscious of the foetal movements and report any sign of decreased activity to the doctor immediately.
Mothers carrying multiple babies have a higher chance of complications during labor and birth than a woman delivering a single baby. Potential complications include a higher risk of prolapsed cord when the water breaks, a placental abruption, particularly after the delivery of the first twin, and postpartum haemorrhage for both vaginal and C-section deliveries.
Practitioners may recommend trying for a vaginal birth as long as:
- The babies are head down or are in the vertex position.
- Neither the mother nor the babies have problems that would make a caesarean section necessary.
Many practitioners feel that a vaginal delivery is a reasonable choice, while others feel that a planned caesarean section is the best way to go.