Written by Dr. Prathima Radhakrishnan on 22 June 2018
Globally there has been a rise in the incidence of twin pregnancies, primarily due to increasing use of assisted reproductive techniques. Maternal, fetal and neonatal mortality and morbidity are significantly higher in twins compared to singletons. Again the complications are three to five folds higher in monochorionic compared to dichorionic twin gestation. Determination of chorionicity aids in risk stratification, performance of invasive procedures, genetic counseling as well as management of complications and thus is of utmost importance in determining pregnancy outcome in twins.
Dichorionic twin gestation Complications:
Management of uncomplicated cases:
Antenatal management plays a key role in detection and prevention of complications associated with twin gestations. The role of ultrasound is paramount in assessment of chorionicity and amnionicity.
Ultrasound and antenatal fetal surveillance of dichorionic twins
1. Early pregnancy scan-diagnosis of multiple pregnancy and counseling
2. 11-14 weeks/ Nuchal translucency scan (NT scan) - confirmation of chorionicity
- screening and diagnosis of chromosomal abnormalities through scan and serum biochemister (First trimester Combined test) and also detection of structural abnormalities
3. Anomaly scan at 20-24 weeks
4. Ultrasound assessment of cervical length
5. Assessment of fetal growth restriction and discordant growth. Fetal surveillance includes frequent nonstress tests with Doppler velocimetry studies
6. Serial growth scans at 24, 28 32 and 36 weeks A dichorionic twin is determined by presence of two discrete placentas, twin peak or lambda sign in the presence of single placental mass, discordant external genitalia and also by assessing the intertwin membrane thickness. Nomenclature is assigned to the babies and documented to assess for consistency throughout the pregnancy. Non stress test (NST) with ultrasound is beneficial in determining amniotic fluid volume and fetal biophysical profile at 34 weeks gestation
ISUOG presents guidelines on management of twin pregnancies:
In clinical practice, delivery of dichorionic twins is recommended by 37-38 weeks of gestation
Intrapartum management strategy includes;
a) Vertex presentation in both twins: Trial of vaginal delivery is attempted irrespective of fetal weight
b) Second twin with non-vertex presentation and fetal weight greater than 2000g: Trial of vaginal delivery is attempted after delivery of first twin.
c) Second twin with non-vertex presentation and fetal weight less than 2000g: Caesarian section recommended
d) Non-vertex first twin, irrespective of second twin presentation: Caesarian delivery recommended
Management of complicated cases
1. Preterm labor: Transvaginal ultrasound to detect cervical length and fetal fibronectin (fFN) aid in predicting onset of preterm labor. Patients with cervical length of ≥3.0 cm and negative fFN are less likely to have premature onset of labor pains. Absolute bed rest is found to be helpful in some cases with significant uterine activity and no change in cervical length. For symptomatic cases of gestational between 24-34 weeks, tocolytics are administered, albeit temporarily, to delay labor and to facilitate corticosteroid administration to augment fetal lung maturity.
2. Fetal structural abnormality: When the fetal anomaly is severe and the parents desire to have a selective fetal reduction, ultrasound guided intracardiac injection of potassium chloride is administered to facilitate the feticide of the anomalous twin. The risk associated with healthy co-twin loss during the procedure is 5% if performed prior to 20 weeks of gestation and is more in later weeks of pregnancy.
3. Fetal karyotype abnormality: Double chorionic villus sampling (CVS)/ double amniocentesis would confirm the fetal karyotype. When there is discordant karyotypic anomaly, management is by selective feticide of the chromosomally abnormal baby.
4. Discordant fetal growth: Monitoring of fetal well being with serial growth scans should include fetal biometry, amniotic fluid assessment by measuring the deepest vertical pool and arterial and venous Doppler. Time of delivery is decided depending on the status of healthy co-twin and risk of preterm delivery.
5. Death of co-twin: Assessment of health status of the surviving twin and evaluation of underlying etiology is important. In the presence of maternal causes, delivery is recommended. In the absence of any obvious cause, pregnancy is continued with close fetal and maternal surveillance for growth and signs of preterm labour. It is recommended to continue till term, especially if the pregnancy is progressing normally.