Obstetrics

In normal pregnancies, ultrasound to be beneficial to the clinical situation two studies need generally be done:

1. One at around 14-16 weeks for evaluation of several foetuses, location of the placenta, existing foetal anomaly, co-existing pelvic pathology.
2. At 30-32 weeks for monitoring growth pattern and confirmation of previous data. Besides these, there are other clinical situations where an obstetrics ultrasound is of benefit.

Focussing

Before starting the examination, it is essential to take the menstrual history and calculate the time since the last menstrual period.

Optimally full bladder for transvesical study. Focusing is done as described previously.

An empty bladder is required for the first-trimester transvaginal study.

Indications for all Trimester scan

First-trimester

1. Pain lower abdomen.
2. Bleeding per vaginum.
3. Abnormal uterine size as determined by bimanual palpation.
4. To re-confirm the condition of already existing pelvic pathology.
5. Study the internal os, cervical canal in case of recurrent first-trimester abortion.
6. For evaluation of foetal anatomical profile by transvaginal ultrasound in a patient who has delivered one or more congenitally anomalous foetus.
7. Following assisted reproductive procedures like IVF-ET, GIFT, etc. for evaluation of site and number of implantation to decide whether foetal reduction might be required or not. 
8. Elderly women to rule out Trisomy 21 by Nuchal translucency.

An operator in the first trimester should look for:

• Gestational sac.
• Identification of foetal pole.
• Presence of cardiac activity and its rating. 
• Nature and frequency of foetal movement.
• Location of chorion frondosum-decidua basalis complex.
• Several foetal echoes.
• Presence rump length for age determination.
• Crown-rump length for age determination.

Second-Trimester

1. Fetal viability
2. Amniotic fluid evaluation
3. Placental localization, character
4. Conditional of cervix, os
5. Gestational age, anomaly

Third-Trimester

1. Assessment of foetal growth,
2. Biophysical profile
3. Behavioural pattern,
4. Determination of foetal weight,
5. Reassessment of liquor volume and
6. Reconfirmation for the absence of congenital anomaly done previously.

Ecotopic Pregnancy

1.4% of all pregnancies are implanted outside the endometrial lining of the uterine cavity of which 98% are within the fallopian tube.

Few causes implicated in tubal implantation include congenital anomalies of fallopian tube-like- diverticula, accessory Astia, and abnormal tubal length. Tubal pathologies in the form of endosalpingitis, endometriosis of endosalpinx or previous tubal infections are also significant causes. The tubal pathologies are not visualized by 2D ultrasound unless the tube contains fluid. However, the latest techniques like hysterosonosalpingography under 3D ultrasound guidance possibly forms the best method in the present time to diagnose such conditions. 

Other varieties of pelvic pathology that partially occlude the tubal lumen by external pressure and cause impaired tubal lumen by external pressure and cause impaired tubal lumen by external pressure and cause impaired tubal motility may result in tubal implantation. Rarer sites of ectopic implantation include the ovary, cervix or anywhere in the abdominal cavity.

Increased incidence of ectopic gestation has been reported in IUCD users and those on low dose progesterone which is thought to alter the endocrine milieu of the tubal lumen. Ectopic pregnancy accounts for 15% of maternal mortality, morbidity. In undetected cases, maternal mortality increases 10-fold when compared to a normal vaginal delivery. Its incidence among infertile patients has also been quite high which could be due to tubal factors common to both situations. The advent of infertility management has increased heterotopic implantation from 1 in 30,000 to nearly 1 in 7,000. The classical clinical triad of pain, vaginal bleeding and adnexal mass are not present in all the patients.

Delayed diagnosis complicates the maternal condition. Ultrasound can diagnose ectopic pregnancy in very early stage by:

1. Locating the ectopic sac with or without cardiac activity,
2. Locating empty endometrial cavity with thickened hyperechoic endometrium containing some fluid- "Pseudo decidual reaction" in a case of positive biochemical pregnancy - even when the ectopic sac is not very well visualized,
3. Locating an intrauterine sac that does not show any embryo (anembryonic pregnancy), disturbed gestational status with irregular sac outline and the open cervical canal (inevitable abortion). In the last case, the complaint of pain, bleeding is attributed to the intrauterine disturbed pregnancy and not to ectopic gestation unless it is due to a rare case of heterotopic pregnancy,
4. Fluid collection in the fallopian tube and POD- tubal abortion.

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