Obstetric Ultrasound Scan

An obstetric ultrasound scan or fetal ultrasound scan uses sound waves to build a picture of the baby in the womb. There are two ways of performing an ultrasound scan:

Transabdominal (through the abdomen): A transducer is placed on the mother’s abdomen.

Transvaginal (through the vagina): A long, thin transducer is covered with a plastic / latex sheath and is inserted into the mother’s vagina.

Most obstetric ultrasound scans are performed via the transabdominal approach. Occasionally, the doctor may use a transvaginal approach in early pregnancy if the transabdominal scan cannot provide a good image. During the second or third trimesters, transvaginal ultrasound scans can measure the length of the cervix more accurately, and this helps to assess the risk of preterm birth.

Obstetric ultrasound scans are not painful. They do not cause harm to the baby even if performed transvaginally, and can be carried out at any stage of the pregnancy. For many women, obstetric ultrasound scans are the highlights of antenatal visits. It is very exciting for expectant parents to see the baby in the womb, waving hands and kicking legs. Apart from being a joyful experience, antenatal ultrasound scans have their own medical purposes, depending on the stage of the pregnancy when the scans are performed.

First trimester scans (6-12 weeks):

To confirm the pregnancy and its location, thus excluding ectopic pregnancy (a pregnancy outside the uterus);

A dating scan to determine the baby’s gestational age and to see if the due date needs to be adjusted according to the ultrasound scan measurements;

To confirm the number of babies;

To make sure the baby is growing well, thus excluding miscarriage;

To measure the baby’s nuchal translucency during an OSCAR test.

Second Trimester Scans (13-28 Weeks):

A fetal structural scan or morphology scan at 20 weeks to examine the baby’s structures in detail to detect any congenital structural abnormalities;

Fetal growth scans to evaluate the growth of the baby;

To measure the mother’s cervical length in those who are at risk of preterm labour.

Third trimester scans (after 28 weeks):

Fetal growth scans to evaluate the growth of the baby, and to measure the amount of amniotic fluid. This is particularly important for mothers who are carrying twins or who have had problems with a previous pregnancy;

To measure the mother’s cervical length in those who are at risk of preterm labour;

To check the position of the placenta. Having a low lying placenta is a reason for Caesarean delivery;

To check the position of the baby when near term. If the baby is not in a head-down position at the end of the third trimester, the obstetrician can discuss with the mother options for delivery.

The fetal structural scan or morphology scan is a special obstetric ultrasound scan, and should be conducted by a maternal fetal medicine subspecialist. With the exception of this scan, we can offer all other obstetric scans.

All our consultation rooms are equipped with an ultrasound scan machine. An overhead monitor is installed in each room so that mothers can watch the entire ultrasound scan examination. Apart from allowing mothers to see the baby, this arrangement also helps the doctor to explain the ultrasound scan examination findings.

Obstetric Ultrasound Scan