Placental reserve for triplets
The possibilities of the uterus and placental blood supply are not limitless: with triplets, the resource has to be divided into three, and placental insufficiency naturally develops more often and earlier than with twins. Clinically, this is manifested by growth retardation, most often disproportionate - one or two fetuses are noticeably more retarded.
Doppler measurements make it possible to distinguish a small fetus, which is simply constitutionally smaller, from a fetus that is actually experiencing oxygen starvation. In a healthy small fetus, resistance indices in the umbilical cord artery remain normal. With true growth retardation, they increase, then diastolic blood flow disappears, and in the middle cerebral artery, resistance, on the contrary, decreases - this is the centralization of blood circulation, a protective reaction in which the fetal body redirects blood to the brain.
The data is assessed in complex for each fetus separately and serves as the basis for the main decision in case of triplets - about the timing of delivery. There is always the same compromise: the longer the pregnancy, the more mature the lungs, but the greater the risk of decompensation for the most vulnerable fetus. Regular Doppler testing is the only way to make this decision in an informed manner.
Chorionicity is the main issue in multiple pregnancy
The prognosis of a multiple pregnancy is determined not so much by the number of fetuses as by the number of placentas and membranes. Dichorionic twins, where each fetus has its own placenta, proceeds relatively well. Monochorionic, where there is one placenta for two, carries the risk of specific complications associated with vascular connections within the common placenta, and requires monitoring every two weeks.
Chorionicity is most reliably determined at 11–14 weeks by the shape of the septal attachment site: the λ-sign indicates dichorionic twins, the T-sign indicates monochorionic twins. After 16–18 weeks, these signs smooth out, and the accuracy of the determination drops sharply. That is why the first study in case of multiple pregnancy is especially important and cannot be postponed.
Specific complications
With monochorionic multiple pregnancy, feto-fetal transfusion syndrome is possible - uneven redistribution of blood between fetuses through anastomoses of the common placenta. One fetus receives excess volume and polyhydramnios, the second receives less and suffers from oligohydramnios and growth retardation. The condition develops quickly and requires timely intervention, so the main way to detect it is regular ultrasounds with measurement of water pockets in each fetus.
The second common problem is selective growth retardation, when one fetus is significantly behind the other. A difference in the calculated mass of more than 20–25 percent is considered significant. Anemia-polycythaemic sequence is also possible, which is detected by the difference in peak systolic velocity in the middle cerebral arteries of the fetuses.
Why does the study take longer?
In case of multiple pregnancy, not one study is performed, but several: a full protocol for each fetus plus a general assessment of the uterus, placenta, septum and cervix. The volume of measurements increases as a multiple of the number of fetuses, hence the longer duration of treatment and higher cost compared to a singleton pregnancy.
An additional complexity is created by the relative position of the fruits: they cover each other, and the doctor has to spend a long time looking for the right cut. Sometimes part of the protocol is postponed for a follow-up visit a few days later - this is common practice and not a sign of trouble.