What should my human chorionic gonadotropin (hCG) level have been at day 28 if it was following the previous pattern of increase, given my history of in vitro fertilization (IVF)?

Expected hCG Level at Day 28 Post-IVF Transfer

Based on your IVF history and previous hCG patterns, your day 28 level should have approximately doubled every 48-72 hours from your earliest measurements, but the specific expected value depends entirely on your initial hCG level at the first measurement (typically day 9-14 post-transfer). 1

Understanding hCG Kinetics in IVF Pregnancies

Normal Rise Patterns in Viable IVF Pregnancies

• In viable intrauterine pregnancies, hCG rises by a minimum of 53% over 48 hours during early gestation, though the median rise is 124% over 2 days 1
• The slowest acceptable rise for a potentially viable pregnancy is 24% at 1 day and 53% at 2 days 1
• After a 5-day blastocyst transfer, day 28 corresponds to approximately 6 weeks gestational age using standard obstetric dating 2

Calculating Your Expected Level

To determine what your day 28 level should have been:

• Start with your earliest post-transfer hCG value (typically measured 9-14 days after a 5-day blastocyst transfer) 2
• Apply the minimum 53% rise every 48 hours to calculate the lower threshold of normal 1
• Apply the median 124% rise (2.24-fold increase) every 48 hours to calculate the expected typical value 1
• By day 28, a viable pregnancy should have hCG levels well into the thousands, typically exceeding 3,000 mIU/mL, at which point a gestational sac should be definitively visible on transvaginal ultrasound 2

Critical Prognostic Factors for IVF Pregnancies

Day 28 Estradiol Levels Matter

• Day 28 estradiol (E2) levels are highly predictive of pregnancy outcomes in IVF 3
• E2 ≤50 pg/mL is associated with only 15.4% live birth rate and 66.5% biochemical pregnancy rate 3
• E2 51-100 pg/mL shows 41.2% live birth rate and 30.7% biochemical pregnancy rate 3
• E2 >100 pg/mL correlates with 77.4% live birth rate, representing the threshold for favorable prognosis 3

hCG Patterns Specific to IVF

• IVF pregnancies show cyclic peaks in hCG during the first 56 days after embryo transfer, a phenomenon not seen in spontaneous conceptions 4
• These cyclic fluctuations may indicate early embryo loss when multiple embryos were transferred 4
• Declines in hCG levels preceded four of five first-trimester abortion peaks in IVF singleton pregnancies 4

When Your Pattern Suggests Problems

Abnormally Low hCG at Day 28

• If your day 28 hCG is <50 mIU/mL, this strongly predicts biochemical pregnancy with decreased odds of live birth 3
• hCG levels that fail to rise by at least 53% over 48 hours indicate nonviable pregnancy 1
• At day 28 (approximately 6 weeks GA), markedly elevated hCG >100,000 mIU/mL may indicate gestational trophoblastic disease or multiple gestation 2, 5

Required Ultrasound Correlation

• At day 28 with appropriate hCG levels (>3,000 mIU/mL), transvaginal ultrasound should show:
  • Definite intrauterine gestational sac 2
  • Visible yolk sac (appears when mean sac diameter >8 mm) 2
  • Cardiac activity should be detectable at 6 weeks gestational age 2

Management Algorithm for Abnormal Patterns

If hCG Rise is Suboptimal

• Obtain repeat serum hCG exactly 48 hours after the previous measurement using the same laboratory 2
• Perform transvaginal ultrasound regardless of hCG level, as 22% of ectopic pregnancies occur at hCG <1,000 mIU/mL 2
• Never defer ultrasound based on "low" hCG levels in symptomatic patients 2

If hCG Pattern Shows Cyclic Decline

• Cyclic declines in IVF pregnancies may indicate early embryo loss, particularly if multiple embryos were transferred 4
• Obtain specialty consultation immediately if hCG plateaus (defined as <15% change over 48 hours for two consecutive measurements) 2

Critical Pitfalls to Avoid

• Do not use a single hCG measurement to predict pregnancy viability—serial measurements 48 hours apart provide meaningful clinical information 2
• Do not rely on the discriminatory threshold of 3,000 mIU/mL alone to exclude ectopic pregnancy, as this has virtually no diagnostic utility (positive likelihood ratio 0.8) 2
• Never assume a viable pregnancy based solely on rising hCG—ultrasound confirmation of intrauterine location and cardiac activity is essential by 6 weeks 2
• Be aware that IVF pregnancies may show higher initial hCG levels if multiple embryos implanted, even if only one survives 4