Ultrasonography as a diagnostic and therapeutic tool has contributed immensely to maternal-fetal medicine. With modern real time equipment it is now possible to obtain high resolution images of the fetal anatomy and to observe the various fetal activities in- utero. The introduction of Doppler scanning enables the study of blood flow in various blood vessels and organs in the fetus and the mother, thereby giving an insight into various aspects of fetal and maternal physiology. Of benefit to the couple is the fact that they can see the fetus moving on the screen and this helps in early maternal–fetal bonding.

What is Ultrasound

The term ultrasound refers to very high-frequency sound waves, which are above the human hearing range.  The use of ultrasound for medically diagnostic purposes was developed from SONAR (sound navigation and ranging) systems used to detect submarines.  The human ear can detect frequencies in the range of 20-20000 Hz. Sound above this range is known as ultrasound. Most instruments used in diagnostic medicine use sound in the range of 1-10 MHZUltrasound is based on the principle that when any form of energy is applied to a quartz crystal it vibrates to produce waves. This wave strikes the various tissues and is reflected back to the quartz crystals, which in turn produces a corresponding electric current. This current is further processed by the machine, to be displayed as images.  The image is displayed in various shades of grey depending on tissue density e.g. bone appears white and fluid appears black. The number of shades of grey displayed by the machine is around 256, as compared to the human eye, which can perceive only 16 shades of grey. This improves the resolution of the picture. 

The procedure

For the purpose of diagnoses ultrasound is performed as an outpatient procedure. For purpose of treatment the patient may be required to stay a few hours in hospital for observation after the procedure. The ultrasound scan may be performed either transabdominally or transvaginally. Trasabdominal (TAS): The patient is instructed to have a full bladder in most cases. The ultrasound probe is placed over the maternal abdomen after applying a gel to the probe. By moving the probe over various areas in the abdomen, all the structures in the abdomen, as well as the fetus and its structure can be studied in detail. Transvaginal (TVS) scanning does not require a full bladder. In fact it is preferable to empty the bladder immediately before the scan. It is better than TAS for early pregnancy evaluation, in obese patients, and for pelvic diseases.  The patient lies in the examination table with her legs bent at the knees or held against her abdomen.  The probe is covered by a condom or rubber sheath. Contact gel is first applied to the probe tip and even on the outside. The probe is gently introduced into the vagina. There is very little discomfort to the patient. It is not acceptable in cases where the hymen is intact. Non-sexually active and postmenopausal women having a transvaginal scan may experience some discomfort. The drawback in transvaginal scans is the limited field of view. Structures 8-9 cms away from the probe may not be visualized properly.


Uses of Ultrasound

1. Obstetric or pregnancy: An ultrasound scan helps identify the following:
   • Presence or absence of a pregnancy – This is done by noting the presence of a gestational sac i.e. the sac that contains the fetus.  The scan also helps identify the location of the pregnancy – whether intrauterine or extrauterine. The latter is referred to as an ectopic pregnancy.
   • Assess the growth and development of the fetus. For the latter all the structures of the fetus are evaluated around 18-22 weeks of gestation. In a transvaginal scan the detailed anatomy can be studied around 14-15 weeks.
   • Placental localization- Normally the placenta is present in the upper part of the uterus.
   • Assess the amount of fluid surrounding the fetus i.e. liquor amnii.
   • In the last few weeks of pregnancy certain features of the fetus such as breathing movement, muscle tone are studied which are indicators of fetal well being. These parameters are included in a method of evaluation termed the biophysical profile.
   • Study of the anatomy of the cervix and its functional capacity in pregnancy.

Uterus & Ovaries as seen on Scan

   2. Gynecological:

• To study pelvic anatomy i.e. uterus and ovaries. Normal tubes cannot be visualized on a scan. When tubes are dilated, they can be seen as fluid pouches or swellings. 
• Presence of masses in the pelvis such as fibroids, endometriosis, large inflammatory masses of the tubes, & ovarian masses – be they cystic or solid, benign or malignant.
• Locate the presence of an intrauterine contraceptive device.
• In infertility – to monitor the growth of the follicles in the ovary.

     3. Interventional procedures

• Oocyte retrieval – removal of the fluid containing the egg from follicles in the process of in-vitro-fertilization.
• Cyst aspiration – removal of fluid from cysts
• Amniocentesis – removal of fluid surrounding the fetus for diagnostic or therapeutic purposes.
• Chorion villus biopsy – removal of tissue from the placenta for prenatal diagnosis.
• Cordocentesis – removal of fetal blood from the umbilical vessel for diagnostic purposes
• Fetal blood transfusion – in cases of Rh incompatibility between the mother and fetus wherein the fetus has been compromised.

    4. Doppler

Safety of ultrasoundNo injurious effects to the mother or fetus have been identified as a result of ultrasound scanning. There have been no unequivocal data to suggest that there is impaired development of hearing, vision, behavior or neurological function due to ultrasound scanning. There is a possible association of left-handedness amongst boys who were subjected to scans in their mothers’ womb.