Diagnosis of twins
The diagnosis of twins is not always easy in primigravidae with firm abdominal walls, or in obese women, and experienced doctors and midwives may not always detect them. The period of gestation is also difficult to assess.
An ultrasonic scan will demonstrate two heads at 15 weeks; two gestational sacs have been seen at eight weeks. X-rays may be used after the 30th week.
Twins may first be diagnosed by finding the uterus large and the fundus well above the umbilicus after the birth of the first baby.
Suspicious is aroused when the uterus is unduly large for the period of gestation after the 20th week. The uterus looks round or broad and fetal movement may be seen over a wide area, but this is not diagnostic. At term, a woman of average build has an abdominal girth of about 100cm. the possibility of polydramnios must be considered, and it can be present in conjunction with or independent of twins, but palpation should help to conclude the diagnosis.
Finding two heads is diagnostic. If one fetus lies in front of the other, it may not be easy to detect two heads or two backs. Should the fetal head seem small in comparison with the size of the uterus this rather suggests the presence of two fetuses. Excessive fetal parts might make one suggest that twins were present.
Hearing two fetal hearts is not a reliable method of diagnosis because with a large, vigorous fetus, the fetal heart can sometimes be heard over a wide area.