OBSTETRIC ULTRASOUND

OBSTETRIC ULTRASOUND (Pregnancy)

Obstetric Ultrasound is the use of ultrasound scans in pregnancy.This is an imaging tool that provides pictures of an embryo or fetus within a woman’s uterus.

Why and when is Ultrasound used in Pregnancy?

1. Diagnosis and confirmation of early pregnancy.

The gestational sac can be visualized as early as four and a half weeks of gestation and the yolk sac at about five weeks. The embryo can be observed and measured by about five and a half weeks. Ultrasound can also very importantly confirm the site of the pregnancy is within the cavity of the uterus. 

2. Vaginal bleeding in early pregnancy.

3. Determination of gestational age and assessment of fetal size.

  

         a.  Crown-rump Length(CRL) 

          Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump). It is typically determined from ultrasound imagery and can be used to estimate gestational age.This measurement can be made between 7 to 13 weeks and gives very accurate estimation of the gestational age.

         b. Bi-parietal Diameter (BPD) 

          The diameter between the 2 sides of the fetal head. This is measured after 13 weeks. It increases from about 2.4 cm at 13 weeks to about 9.5 cm at term.

         c. Femur Length(FL)

       Measures the longest bone in the body and reflects the longitudinal growth of the fetus. Its usefulness is similar to the BPD. It increases from about 1.5 cm at 14 weeks to about 7.8 cm at term.

         d.Abdominal circumference(AC)

       The distance around the outer edge of a developing baby's abdomen. The single most important measurement to make in late pregnancy. It reflects more of fetal size and weight rather than age. Serial measurements are useful in monitoring growth of the fetus.

4. Diagnosis of fetal malformation. 

5. Placental localization.

      The placenta is the organ which transfers oxygen and nutrients from the mother’s blood into the baby’s blood. It is connected to the mother’s uterus over a wide surface area. The baby is connected to the placenta via the umbilical cord.The placenta can be situated anywhere on the surface of the uterus.Ultrasound is used to determine the location of the placenta and its proximity to the cervix. It can change during the pregnancy for a number of reasons.

 

6. Multiple pregnancies.