After our 32 week appointment with my OB, we had a follow up appointment at maternal fetal medicine due to the twins’ weight discrepancy and Twin A’s small size. I had a pretty detailed ultrasound, looking at each baby’s organs, growth, cord blood flow, and amniotic fluid. Everything looked good, and there were a few surprises. I got to see a baby drinking amniotic fluid, holding her leg, licking her hand and cord, etc.
It also appeared that I might only have one placenta, which would make the babies mo/di and not di/di. It is also another argument for a c-section. Either way, there is a 33% chance that our babies are actually identical.
Zygosity (twin type) is not as simple as having 1 or 2 placentas. According to Multiples of America, “more important than the placenta itself are the fetal membranes, which can be helpful in determining twin type. They are the thin membranes filled with fluid that surround the fetus and are attached to the placenta. The amnion is the inner membrane, and the chorion is the outer membrane. A shared amnion always means monozygotic twins, but is very rare. Two amnions and one chorion also means monozygotic twins. If there are two amnions and two chorions the twin type can be either mono- or dizygotic.
Fraternal or dizygotic twins will always have two placentas, as the two eggs implant separately into the uterus. However, if the eggs implant close together the placentas can become fused and take on the appearance of one placenta. Twins can then be mislabeled monozygotic.
However, identical twins do not always have one placenta. Monozygotic twins come from an egg that splits into two. The timing of the split will determine the number of placentas. If the split happens after the egg has already implanted into the uterus, there will be one placenta. If the split happens earlier, before implantation, then the two eggs can implant separately into the uterus and form two separate placentas. The twins will still be identical.”
Derek and I met with the director of fetal medicine, and he felt that at this point we don’t have need for concern about the babies’ sizes or discordance. The babies were 4 pounds 10 ounces and 4 pounds 9 ounces. This puts them in the 21st and 20th percentiles respectively, and obviously doesn’t show much weight discordance. The doctor gave us some information about why the weight formulas have a 15% margin of error. Bone measurements are fairly accurate measurements, but a squishy abdomen is not. If a baby is getting squished, then this part of the formula could be off. He also stressed that again the percentiles are compared to singletons and twins tend to be smaller.
The doctor said that they really only start worrying if the babies’ weights are 20% apart, a baby suddenly just stops growing, there isn’t good cord blood flow, or there isn’t enough amniotic fluid. When there isn’t enough cord blood flow, the blood goes to the brain and the heart and the other organs and limbs don’t grow; the kidneys don’t process as much amniotic fluid, which manifests as a low fluid pocket for the baby.
As our babies aren’t presenting with any of these issues, he recommended that I only need to see my OB once a week for non-stress tests (NSTs), which measure fetal movement, fetal heart rate, and uterine contractions, or biophysical profiles (BPPs), which is an ultrasound to measure amniotic fluid, fetal muscle tone, fetal heart rate, and fetal breathing. At this point, the doctor does not feel that we need to consider delivering the babies early to get them more nutrients outside the womb. As well, I do not need to have extra appointments with the OB or fetal medicine. We will have another growth ultrasound at 36.5 weeks.