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Mono/Mono Twins

The following is intended to help our family and friends understand my high-risk pregnancy and why I have been in the hospital for about a month and why the babies will be born early. If you search some of the terms I’ve described below, you will find much interesting and differing information about this condition, but my description below represents what Scott and I have learned and accepted from our many doctors. Thank you for all your love and support throughout this trying time and we appreciate your ongoing prayers for our growing little family.
What are Mono/Mono Twins?
Our babies are monoamniotic/monochorionic (mono/mono) twins. This means they are developing within the same amniotic sac. A rare occurrence, most of the literature says it accounts for only about 1% of identical twin gestations. It occurs when the egg splits after the amniotic sac has already formed around it (normally the egg will split earlier, allowing an amniotic sac to form around each fetus). Each baby has her own umbilical cord that attaches to the same placenta, which is her source of nourishment.

 Mono/mono twins are a complicated pregnancy because of the high-risk of fetal death due to umbilical cord entanglement (added to the regular risks of a multiple gestation). Since there is nothing to separate the babies, there is nothing to keep them from twisting around each other and tangling and knotting their cords. Twists and knots in their cords can easily cut off the blood supply to one or both of the babies. Cord entanglement can cause a slow reduction in blood flow creating problems over time or cause a sudden complete loss of blood flow in a matter of minutes or seconds.

The statistics on this condition vary depending on which study or website you read, but the most widely reported and accepted number is that mono/mono babies have a 50% fetal mortality rate.

For the first couple of months, there isn’t anything you can do but pray. Once the babies reach what the doctors call viability – the age at which the babies could survive outside of their mother – you can take an active role in monitoring them and intervening if necessary. Weighing the risks of prematurity against the risks of loosing the babies, parents must decide if, when and how often to monitor the babies for signs of distress. Fetuses become “viable” at about 26 weeks, so many doctors recommend checking into the hospital for inpatient fetal monitoring after that point so they can perform an emergency delivery if the babies become distressed.

As the weeks go by, the risks of prematurity go down significantly, but the risks of cord entanglement do not change. Because of the constant risk, most doctors recommend elective delivery at 32-34 weeks. (For reference, a full-term pregnancy is 40 weeks.) At 32 weeks the babies have an excellent chance not only for survival, but also for a normal, healthy life. Some women and their doctors are comfortable going to 34 weeks before delivery (usually with monitoring many times a day or 24/7 monitoring).

Since this is a rare condition, there is little data and much debate on treatment and outcomes. Because there are limited cases and ethical issues associated with studying pregnant women, not many studies exist. Those that have been done use data on documented cases from the previous ten to fifteen years.  A couple recent papers show that intensive inpatient fetal monitoring dramatically increases the odds of delivering two live babies. Also, some studies and anecdotal evidence from women’s stories that I have read online show that it is quite possible to have a bad outcome after 32 weeks. 

Our Story

Week 5: We found out I was pregnant with twins via ultrasound and the doctor thought they were monoamniotic.

Weeks 7-20: Our twins were confirmed as monoamniotic through numerous doctor appointments and ultrasounds. At those appointments with my obstetrian we did discuss the need to deliver earlier than usual due to possible cord entanglement, but were not really informed of the risks or alternative treatments.

Week 20: We confirmed the twins are girls.

Week 22:  We toured the neonatal intensive care unit (N.I.C.U.) at the hospital where we were going to deliver. The tour was comforting in many ways, but it got me questioning the risks and delivery schedule.

Weeks 23-24: We did much internet research and were highly distressed by the information we read, such as the 50% mortality rate and the recommendation for inpatient monitoring.

Week 24: I went to see a perinatologist (also called a maternal fetal medicine (MFM) doctor), which is an obstetrian who specializes in high-risk pregnancies. I expected him to tell me not to believe all the stuff I read on the internet, but he did not. He confirmed most of what I had read.

Week 24: We consulted a neonatologist (a doctor who specializes in preemies and other high-risk or special needs infants) to discuss the risks of premature delivery and how those risks change with gestational age.

Week 25-28: We had weekly appointments and ultrasounds at the MFM clinic. Considering both the MFMs’ and the neonatologist’s recommendations, we decided on a treatment plan: check into the hospital at 28 weeks and deliver at 32 weeks, accepting that the babies could be delivered at any time if they appeared to be in distress and that even at 32 weeks they would be in the NICU for a while.

Week 28: I checked into the hospital for inpatient monitoring. My mom flew in from Virginia to stay with Scott and Reed.

Weeks 28-31: The babies were monitored three times a day using the fetal heart rate monitor and had weekly ultrasounds. When something abnormal or inexplicable appeared during the monitoring, the doctors would order additional monitoring and ultrasounds.

Week 31:  Due to a couple of decelerations in the babies’ heart rates, the doctors moved me to the Labor and Delivery Department for continuous, 24-hour monitoring. For the most part, the girls have looked great on the monitor. They have had a couple more decelerations in their heart rates, but nothing to cause an emergency delivery.

Week 32:  Delivery is scheduled for the morning of May 6th.

Weeks to come: The babies will be in the NICU for a period of time, but we won’t know how long until after they are born. 

Fetal Heart Rate Monitor

Fetal Heart Rate Monitor

On the Monitor

On the Monitor

Types of Twins

Twins can occur in one of two ways:

1. Dizygotic Twins (Fraternal)

The more common way is for two different sperm to fertilize two different eggs, resulting in what is called a dizygotic (DZ) twin gestation. These twins are often called fraternal twins. In this type of twinning each twin has its own sac of amniotic fluid and its own placenta (afterbirth). Dizygotic twins have two sets of membranes surrounding their amniotic fluid sacs (one inner amnion layer and one outer chorion layer), and therefore they are known as diamniotic, dichorionic.



2. Monozygotic Twins (Identical)  

Less commonly, twin pregnancy occurs when one sperm fertilizes one egg, but this splits into two embryos resulting in what is known as monozygotic (MZ) twins. These twins are often referred to as identical twins since they have the same genetic material. Approximately one-third of MZ twins look just like fraternal twins on prenatal ultrasound since there are two separate amniotic sacs and two separate placentas. However, in two-thirds of identical twins, each twin has its own amniotic sac but shares a common placenta. This type of MZ twinning is called monochorionic, diamniotic since there is an inner layer surrounding the amniotic sac of each twin, but there is only one common outer layer (chorion) surrounding both of the sacs. Monochorionic twins are at higher risk for complications since they share a common placenta.



Finally, less than one percent of identical twins will have one amniotic sac and one placenta for both twins. This type of twinning is referred to as monchorionic, monoamniotic twinning. These twins are not only at a high risk for complications since they share a common placenta, but are also at very high risk for loss of the pregnancy due to entangled umbilical cords.



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