Obstetric Ultrasound

Objectives and structure of prenatal screening

Screening examinations for pregnant women are performed in expert-level medical institutions (recommendation grade C). Comprehensive diagnostics are aimed at obtaining objective information on the intrauterine state of the fetus and include several mandatory components:

1. Ultrasonography. Assessment of fetal anatomy, placental structure, and screening for aneuploidy markers.
2. Maternal serum biochemical screening. Determination of specific serum markers: pregnancy-associated plasma protein A (PAPP-A) and free beta-subunit of human chorionic gonadotropin (β-hCG).
3. Computerized risk calculation. Based on the obtained data, specialized software calculates the probability of giving birth to a child with chromosomal disorders, as well as the risks of fetal growth restriction (FGR), preeclampsia (PE), and preterm birth (PTB).

An additional option is non-invasive prenatal testing (NIPT). This method allows for the high-accuracy exclusion of aneuploidies by analyzing cell-free fetal DNA circulating in the maternal bloodstream.

First-trimester ultrasound (11–14 weeks)

At this gestational age, the primary objective is to detect major developmental malformations, such as organ agenesis, major skeletal anomalies, and central nervous system defects (anencephaly, meningocele, large encephaloceles).

In the first trimester, special attention is paid to echomarkers of chromosomal pathology:

• Increased nuchal translucency (NT). This is a critical ultrasound marker representing an anechoic fluid collection between the skin and the soft tissues of the fetal cervical spine. Visually, it may present as nuchal edema.
• Agenesis or pronounced aplasia of the nasal bone.
• Discrepancy between the crown-rump length (CRL) of the embryo and the expected gestational age (decreased).
• Enlargement of the urinary bladder (megacystis).
• Presence of an omphalocele (umbilical cord hernia).
• Non-immune fetal hydrops.

Second-trimester ultrasound (18–21 weeks)

By mid-pregnancy, fetal organs are sufficiently formed to diagnose almost all potential developmental anomalies. The spectrum of detectable ultrasound signs indicating chromosomal disorders expands significantly.

Key pathology markers in the second trimester:

• Changes in skull shape and brain structures: characteristic "strawberry" and "lemon" signs of the cranial bones, as well as the "banana" sign indicating an abnormal cerebellar shape. Additionally, the presence of choroid plexus cysts in the lateral ventricles and signs of ventriculomegaly are evaluated.
• Internal organ anomalies: pyelectasis (dilation of the renal pelves), echogenic bowel.
• General abnormalities: cystic hygroma, persistent non-immune fetal hydrops, and symmetric fetal growth restriction (FGR).

Note: certain chromosomal abnormalities, such as Turner syndrome (karyotype 45,X0), may be accompanied by lymphostasis (lymphedema), scoliosis, coarctation of the aorta, and urinary tract anomalies (e.g., horseshoe kidney), which requires a careful dynamic assessment of anatomy.

Invasive methods and examination of the pregnant woman

When non-invasive methods indicate a high risk of genetic abnormalities, invasive prenatal diagnostic methods are applied. In the case of assisted reproductive technologies, preimplantation diagnostic methods can be identified on microphotographs:

• Embryo biopsy: retrieval of genetic material using a micropipette at the 8-blastomere stage.
• Polar body biopsy: extraction of material from the oocyte or zygote.

In addition to high-tech screening, classical methods of examining the pregnant woman remain mandatory components. The physician must be proficient in external obstetric examination techniques, as well as the rules and techniques of pelvic measurement (pelvimetry).

Class and exam questions

What else to study on this topic

• Biochemical screening: interpretation of PAPP-A and free β-hCG levels
• Non-invasive prenatal testing (NIPT): indications and limitations
• Technique and methods of external obstetric examination (pelvimetry)
• Invasive prenatal diagnostics: embryo and polar body biopsy
• Ultrasound diagnosis of developmental dysplasia of the hip (DDH) in newborns
• Radiological and clinical signs of Turner syndrome

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.