Radiodiagnosis
Obstetric and Gynaecological Imaging
Obstetric and gynaecological imaging for MBBS and NEET-PG: early pregnancy ultrasound, ectopic and molar pregnancy, anomaly scan and the PC and PNDT Act, mapped to NMC codes RD1.
MedNext Academy | 3 min read
Obstetric and Gynaecological Imaging
Obstetric and gynaecological imaging for MBBS and NEET-PG: early pregnancy ultrasound, ectopic and molar pregnancy, anomaly scan and the PC and PNDT Act, mapped to NMC codes RD1.
This chapter covers imaging in pregnancy and gynaecology, where ultrasound is the safe and central modality. It teaches the milestones of early pregnancy, the diagnosis of ectopic and molar pregnancy, the screening and anomaly scans, Doppler assessment of the foetus, and the medicolegal framework of the PC and PNDT Act.
High-yield: Obstetric and Gynaecological Imaging
- Ultrasound is the primary imaging modality in obstetrics and gynaecology because it is real time, safe and free of ionising radiation.
- Transvaginal ultrasound gives higher resolution of the early pregnancy and pelvic organs than the transabdominal approach.
- The gestational sac is seen from about five weeks, the yolk sac soon after, and cardiac activity from about six weeks on transvaginal scan.
- An empty uterus with a positive pregnancy test and a beta-hCG above the discriminatory level raises concern for an ectopic pregnancy.
- A tubal ring or adnexal mass separate from the ovary with free fluid supports the diagnosis of ectopic pregnancy.
- A snowstorm or bunch-of-grapes appearance of the uterine cavity suggests a hydatidiform mole.
- The dating scan in the first trimester uses the crown-rump length, the most accurate measure of gestational age.
- The nuchal translucency measured between 11 and 14 weeks screens for chromosomal abnormality when increased.
- The anomaly scan is performed around 18 to 20 weeks to assess foetal structure and detect major malformations.
- Placenta praevia is diagnosed when the placenta covers or lies close to the internal cervical os, requiring assessment before delivery planning.
- Doppler ultrasound of the umbilical and middle cerebral arteries assesses foetal wellbeing in growth restriction.
- The PC and PNDT Act prohibits the use of ultrasound for sex determination of the foetus, and non-compliance carries penalties.
- Ultrasound characterises ovarian cysts and masses, and MRI is used to further evaluate complex adnexal masses and stage gynaecological cancer.
- Hysterosalpingography assesses tubal patency and the uterine cavity in the investigation of infertility.
Ultrasound milestones and safeguards
- **Early pregnancy:** Gestational sac from about 5 weeks, cardiac activity from about 6 weeks.
- **Dating and screening:** Crown-rump length for dating; nuchal translucency at 11 to 14 weeks.
- **Ectopic pregnancy:** Empty uterus with positive test above the discriminatory beta-hCG; adnexal mass.
- **PC and PNDT Act:** Sex determination of the foetus by ultrasound is prohibited by law.
NMC competencies in this chapter
- **RD1.4:** Radiological investigation and interpretation in common obstetric and gynaecological conditions
- **RD1.13:** Components of the PC and PNDT Act and its medicolegal implications
Frequently Asked Questions
Why is ultrasound the main modality in pregnancy?
It uses no ionising radiation, is real time and portable, and gives excellent images of the foetus and pelvic organs, making it safe for repeated use throughout pregnancy.
How is an ectopic pregnancy suggested on ultrasound?
An empty uterus with a positive pregnancy test and a beta-hCG above the discriminatory level is suspicious, especially with an adnexal mass or tubal ring separate from the ovary and free pelvic fluid.
What does the PC and PNDT Act prohibit?
It prohibits the use of ultrasound or any technique for prenatal determination of foetal sex, to prevent sex-selective abortion. Contravention carries legal penalties for the doctor and the facility.
What is the most accurate way to date a pregnancy?
The crown-rump length measured on a first-trimester ultrasound is the most accurate measure of gestational age, more reliable than later biometry for dating.
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