Diagnosis of pregnancy

Tests of ovarian functional diagnostics

Assessment of the reproductive system state and indirect diagnosis of early pregnancy are based on confirming the biphasic nature of the menstrual cycle.

• Basal body temperature. Measured rectally, daily in the mornings, strictly before getting out of bed. Normally, before ovulation it is below 37 °C, during ovulation it rises to 37.6–37.8 °C, and subfebrile values persist during the second phase. Upon pregnancy, no premenstrual drop occurs — the temperature remains subfebrile due to the influence of progesterone.
• Pupil symptom. Reflects the level of cervical mucus secretion under the influence of estrogens. Maximum gaping of the external os (evaluated as "+++") is observed during ovulation.
• Mucus stretching symptom. When the instrument blades are separated, the length of the mucous strand at the moment of ovulation reaches a maximum — 10–12 mm.
• Caryopyknotic index (CPI). A cytological indicator of a vaginal smear. Demonstrates the ratio of superficial cells with pyknotic nuclei to the total number of epithelial cells. A peak (80–88%) indicates the maximum estrogen level in the body.

Note: The biphasic nature of the cycle can be reliably confirmed only through histological examination of the endometrium.

Impact of toxic factors on the embryo and fetus

When confirming pregnancy, it is extremely important to exclude the influence of damaging factors. The degree of their impact always depends on the dose and duration.

• Ionizing radiation. In early stages, it causes the death of the embryo, during the period of organogenesis it leads to developmental anomalies (the CNS and vision are especially sensitive), and after the 12th week it provokes fetal growth restriction (FGR) and symptoms of radiation sickness.
• Nicotine. Freely crosses the placental barrier. It does not have a teratogenic effect, but causes powerful vasospasm and blocks amino acid transport. The result is chronic placental insufficiency and pronounced FGR.
• Alcohol. Is a strict teratogen. Due to the absence of the alcohol dehydrogenase enzyme in the fetal liver, the toxicity of ethanol increases manifold, forming fetal alcohol syndrome (microcephaly, heart defects, cranial anomalies).
• Narcotic substances. Cocaine causes acute circulatory disorders, intestinal infarctions, and intracranial hemorrhages with the formation of porencephalic cysts.

Pharmacotherapy and the placental barrier

Placental permeability to drugs depends on their molecular weight and gestational age (maximum is reached by the 32nd week). Drugs with a high molecular weight (sodium heparin, insulin) do not cross the placenta.

According to the FDA classification, drugs are divided into five categories: from A (safety proven, e.g., iron preparations) to X (strictly contraindicated, risk outweighs benefit).

Hazardous drugs:

1. Tetracyclines — damage tooth buds and the skeletal system.
2. Aminoglycosides — cause irreversible deafness.
3. Indirect anticoagulants (warfarin) — provoke skeletal anomalies.

Approved drugs: Penicillins, cephalosporins, as well as direct-acting anticoagulants (low-molecular-weight heparins).

Class and exam questions

What else to study on this topic

• Histological examination of the endometrium for precise confirmation of cycle biphasicity.
• Specific neonatal abstinence syndrome in newborns from substance-dependent mothers.
• The effect of anticonvulsant drugs on the fetus and prevention of hemorrhages with vitamin K.
• Maternal physiological adaptation to pregnancy and features of fetal circulation.
• Principles of prescribing hormonal drugs (progesterone, glucocorticoids) during pregnancy.

Other topics in the "Obstetrics" section

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