Diagnosis of pregnancy | Medical Science Optional Notes for UPSC PDF Download

Clinical signs and symptoms of pregnancy

• Amenorrhea:
  • The sudden halt of menstruation in a healthy reproductive-aged woman, previously experiencing regular menses, strongly indicates pregnancy.
• Uterine Bleeding:
  • In some cases, uterine bleeding may occur post-conception, mimicking menstruation. During the first month, such occurrences are often related to blastocyst implantation.
• Lower-Reproductive-Tract Changes:
  • Vaginal mucosa takes on a dark bluish-red and congested appearance, known as Chadwick sign.
• Changes in Cervical Mucus:
  • Elevated progesterone levels in pregnancy alter the consistency and microscopic appearance of cervical mucus.
• Uterine Changes:
  • Early Weeks:
    • Uterine size increases primarily in the anteroposterior diameter.
    • Bimanual examination reveals a doughy or elastic feel.
  • 6 to 8 Weeks' Menstrual Age:
    • Firm cervix contrasts with the softer fundus.
    • Compressible softened isthmus is evident—Hegar sign.
  • Marked Isthmic Softening:
    • Isthmic softening can be so pronounced that the cervix and uterine body seem distinct.
  • 12 Weeks' Gestation:
    • Uterine body becomes almost globular with an average diameter of 8 cm.
  • Later Pregnancy:
    • Auscultation with a stethoscope may reveal the uterine souffle.
    • This soft, blowing sound, synchronous with the maternal pulse, results from blood flow through dilated uterine vessels. It is most distinct near the lower part of the uterus.

Human Chorionic Gonadotropin (hCG): Structure, Measurement, Function, and Assessment

Structure

• HCG is a glycoprotein characterized by a high carbohydrate content.
• It consists of two noncovalently linked subunits, labeled as alpha (α) and beta (β).
• The alpha (α) subunit is identical to those found in luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH).

Measurement of hCG

• HCG has an alpha (α) and a structurally distinct beta (β) subunit.
• Antibodies with high specificity for the hCG beta (β) subunit have been developed, enabling the detection of hCG.
• Various commercial immunoassays are available for measuring serum and urine hCG levels.

Function

• HCG plays a crucial role in preventing the involution of the corpus luteum, the primary site of progesterone formation in the first 6 weeks of pregnancy.
• The syncytiotrophoblast produces increasing amounts of hCG during the first trimester after implantation.

Assessment

• Sensitive tests can detect hCG in maternal serum or urine approximately 8 to 9 days after ovulation.
• The serum hCG concentration doubles with a time frame of 1.4 to 2.0 days.
• Peak levels of serum hCG are reached at 60 to 70 days after implantation.
• Subsequently, the concentration gradually decreases, reaching a plateau around 16 weeks.

Laboratory Sensitivity

• Sensitivity for laboratory detection of hCG in serum is as low as 1.0 mlU/mL using this method.
• Extremely sensitive immunoradiometric assays can detect hCG at an even lower limit.

False Results

Home Pregnancy Tests based on urine levels of beta HCG-Limitations

• Market Scale: Millions of over-the-counter pregnancy test kits are sold annually.
• Detection Limit Study: A study by Cole and associates in 2011 found that a detection limit of 12.5 mlU/mL is required to diagnose 95 percent of pregnancies at the time of missed menses.
• Brand Sensitivity: Only one brand demonstrated the required sensitivity, while two other brands yielded false-positive or invalid results.
• False Positives at 100 mlU/mL: Even at an hCG concentration of 100 mlU/mL, only 44 percent of brands displayed clearly positive results.
• Limited Diagnosis Window: Only about 15 percent of pregnancies could be diagnosed at the time of missed menses, given the observed sensitivities.
• Manufacturer Claims: Some manufacturers of newer home urine assays claim >99-percent accuracy on the day of, and some up to 4 days before, the expected day of menses.
• Actual Sensitivity Analysis: Despite manufacturer claims, careful analysis suggests that these assays often do not exhibit the advertised level of sensitivity.

Diagnosis of pregnancy

Normal Pregnancy

• hCG Concentration:
  • Doubles every 2.5 days in early pregnancy.
  • Peaks at 10 weeks of gestation (~100,000 mlU/mL) and then declines.
• Transvaginal Ultrasound Visibility:
  • Pregnancy is visible with a transvaginal ultrasound at a beta-hCG level of 1,500-2,000 mlU/mL.
  • If beta-hCG is <1,000 mlU/mL, repeat beta-hCG and transvaginal ultrasound in 2-3 days.

Abnormal Pregnancy

• Low or Slow Rise in Values:
  • Indicates ectopic pregnancy or abortion.
• High or Fast Rise in Values:
  • May indicate beta-hCG-secreting tumors (hydatidiform mole, choriocarcinoma) or twin pregnancy.
  • Trophoblastic diseases show a level of >40,000 mlU/mL.
  • In metastatic cases of malignant GTD:
  • Serum hCG levels between (40,000-50,000 mlU/mL) or urine hCG levels <1,000 IU/24 hours indicate good prognosis.
  • High serum hCG level (>50,000 mlU/mL) indicates a poor prognosis.

Diagnosis of Pregnancy: Ultrasound Findings in Normal Pregnancy (Abdominal or Transvaginal)

• 5-6 Weeks of Pregnancy:
  • Detection of the embryo.
• 10-12 Weeks of Pregnancy:
  • Detection of fetal heartbeat with Doppler ultrasound.
• 18-20 Weeks of Pregnancy:
  • Observation of fetal movements.
  • These diagnostic indicators aid in assessing the progression of a normal pregnancy and identifying potential abnormalities.

Diagnosis of pregnancy-Repeats

Q1: Write a short note on Methods of Diagnosis of Pregnancy? (2005) 

Q2: A lady comes with 2 months of amenorrhoea to the antenatal clinic. How would you diagnose pregnancy in her? (2009). 

Q3: How does the pattern of rise in human chorionic gonadotrupin (HCG) differ between a normal and abnormal pregnancy? How accurate are most home pregnancy tests? What are the most common causes of false positive and false negative pregnancy tests? (2018)