Complications specific to multiple pregnancy
Some pregnancy complications only occur in twin and multiple pregnancies. These include selective intrauterine growth restriction (IUGR), Twin-to-Twin Transfusion Syndrome (TTTS) and cord entanglement in twins who share an amniotic sac.
Twin-to-Twin Transfusion Syndrome (TTTS)
Twin-to-Twin Transfusion Syndrome (TTTS) is a rare complication of twins and higher gestation pregnancies. The lives of both twins are endangered by this condition, and complications for surviving babies can include cerebral palsy. Treatment of TTTS with the laser fetoscope, available at Auckland Hospital, improves the survival rate of both twins to 50-60%, with a 75% chance that at least one twin will survive.
Early diagnosis of chorionicity is vital to detect TTTS. Dr Emma Parry, the Multiples NZ medical advisor, emphasises the need for early diagnosis of twin type (chorionicity) and regular scanning to identify the potential for problems early in the pregnancy:
About one-quarter of all twin pregnancies share a placenta. If you have a scan that shows you are having twins or higher-order multiples, it is important to find out if they are sharing a placenta before 16 weeks gestation, because after this scans are not accurate enough to diagnose whether the placenta is shared.
Dr Parry has devised a Guideline for the Management of Monochorionic Twins, where she discusses TTTS, and indicates that women who have been diagnosed with a monochorionic twin or multiple pregnancy need to have regular scans beginning at 16 weeks gestation, not the usual 20 weeks for twins who do not share a placenta. Dr Parry states that women also need to know the warning signs for TTTS:
Between 16 to 28 weeks, watch for a sudden increase in the size of your abdomen and shiny red skin, with a feeling of it being stretched or tight. If this happens, your doctor or midwife needs to arrange an urgent scan to assess what is happening.
Selective intra-uterine growth restriction (sIUGR)
Intrauterine growth restriction (IUGR) occurs in 3-10% of singleton pregnancies, 9% of twin pregnancies and 9.9% of monochorionic twin pregnancies. A fetus suffering from IUGR will be small for its gestational age and not growing at the normal, expected rate. IUGR, thought to be a result of problems with the placenta, can also be caused by health problems in the mother. It is diagnosed by ultrasound scanning of the babies’ growth. A difference in the rate of growth between the babies (growth discordance) in the first trimester may also indicate anatomical and chromosomal abnormalities.
Up to 32 weeks gestation, the growth rate for twins should be the same as for singletons, but after 32 weeks growth slows due to the restricted space in the womb/uterus and placental insufficiency—it is overworked growing twins! In triplets, this process starts earlier. The degree of difference in growth (growth discordance) between twin or multiple babies can indicate the degree of the IUGR:
- Mild is less than 15% difference
- Moderate is between 15-30% difference
- Severe is more than 30% difference.
When evaluating the babies’ growth in a multiple pregnancy, it is important to know whether the twins are identical (chorionicity), as they are at a greater risk of IUGR which may be due to placental insufficiency, unequal placental sharing (ITP), placental cord abnormalities and TTTS. IUGR may affect one twin in 12-25% of pregnancies, especially with TTTS, where the difference in growth in the donor twin can be can be up to 85%. The complications of growth restriction that affects only one twin (selective IUGR, or sIUGR), include intrauterine death, which may cause the death or disability of the co-twin, or premature labour.
Abnormal growth discordance can occur in up to 30% of twin pregnancies, but most twins do well despite it. In the second trimester, treatment options include selective termination if one twin is abnormal, so that there is less risk of adverse impact on the co-twin. Should one twin die in-utero, the specialist team aims to get the pregnancy to 34 weeks before delivering the co-twin.
The management of a multiple gestation with severe growth discordance in the third trimester is fairly complex, and involves:
- Serial growth scans (ultrasounds every 1-2 weeks)
- Doppler blood flow studies (ultrasound procedure to measure the blood flow through the placental blood vessels)
- Cardiotocographs (CTG fetal monitoring)
- Possible admission for surveillance
- Giving steroids between 24 and 34 weeks for fetal lung development.
If TTTS or placental cord abnormalities are involved, there are two main treatment options:
- Umbilical cord occlusion (via laser, bipolar coagulation or fetoscopy) for selective reduction (feticide) in order to save the co-twin from death or harm
- Selective Laser Photocoagulation of Communicating Vessels (SLPCV), a new treatment for severe TTTS, which may allow both twins to survive, and benefit the smaller twin. Studies into this area of fetal medicine continue.
To find out more about Intrauterine growth restriction, click here.
Cord entanglement in identical twins who share the same sac (monoamniotic twins)
The umbilical cords run from each baby to the placenta, on the wall of the uterus. They feed nutrients, oxygen and blood flow between the babies and the mother. By the time a fetus is full-term, its umbilical cord is around 50 cm long, allowing freedom for the fetus to move inside the womb. Any baby can get tangled in their own cord and there is a risk of compressing the cord (thus, cutting off the supply of nutrients, oxygen and blood) once the membranes have ruptured (during labour) and there is no longer as much fluid to cushion the cord. This risk occurs for each baby during a multiple birth.
So long as each baby in a multiple pregnancy has its own amniotic sac, they are at no risk of becoming tangled in their sibling’s cord. In a monoamniotic pregnancy, however, because the babies share a sac, the risk of cord entanglement is greater, as each baby is not only at risk of getting tangled in their own cord, but of also getting tangled in their sibling’s cord. Cord entanglements (also called ‘Cord Accidents’) are the number one risk in this type of pregnancy.
To put this danger in perspective, virtually all cases of monoamniotic twins will have tangled cords. In order for entanglement to become dangerous, there must also be cord compression. It is very possible to have entanglement apparent as early as 10 weeks (and probably even earlier), and still have both babies born safely at 34 weeks with no complications. Nevertheless, as cord entanglement is the first sign of possible problems, expect the obstetricians to be on high-alert for it.
There are many pictures of cord entanglement on the Monoamniotic Monochorionic Support website (www.monoamniotic.org) that show the level of entanglement that babies can survive through. It may be comforting for some expectant parents to view these, but keep in mind that the pictures are graphic and disturbing.
The only treatment doctors can offer is expediting the birth. If serious problems are discovered before 24-26 weeks (the point of viability outside the womb), there is, sadly, nothing that can be done. After that point, if life-threatening problems are discovered, the babies can be born—although the earlier the birth occurs, the higher chance that the babies may suffer from complications due to extreme prematurity.
While some cord accidents are sudden, it appears that the majority of fatal cord accidents are gradual. Ultrasound, Doppler-imaging (a way of seeing actual blood flow through the cords), and fetal monitoring (CTGs) enable early detection of possible problems. This means that if you are watching often enough, signs of cord compression may be detected early enough to perform an emergency birth, before it is too late.
So, the key to managing a monoamniotic pregnancy is frequent assessment and monitoring. “How much, and how often”, is a question that you will have to address with your obstetrician. Generally speaking, more is better.
For more information about the management of monoamniotic pregnancy, click here.
You may also be interested to read Jocasta’s story—Monoamniotic Twins.