Normal Amniotic Fluid at 13-14 Weeks Gestation
At 13-14 weeks gestation, a single deepest vertical pocket (Maximum Vertical Pocket, MVP) of ≥ 2 cm is considered normal and should be documented on transabdominal ultrasound. 1, 2
Measurement Technique
Position the transabdominal ultrasound probe perpendicular to the uterine contour and parallel to the maternal sagittal plane, measuring the maximal vertical depth in centimeters while excluding umbilical cord and fetal parts. 1
Systematically scan all uterine regions to ensure the deepest pocket is identified—this is critical at early gestational ages when fluid distribution may be uneven. 1
Record vertical depth only; horizontal dimensions are not included in MVP measurement. 1
Normal Values and Clinical Thresholds
MVP ≥ 2 cm is normal at any gestational age, including 13-14 weeks. 1, 2
MVP < 2 cm defines oligohydramnios and warrants further evaluation, even in the first trimester. 1, 2
At this early gestational age, the amnion is typically visualized by 7 weeks and should be clearly seen as a thin membrane surrounding the embryo within the gestational sac. 3
Why MVP Rather Than AFI at This Gestational Age
The Amniotic Fluid Index (AFI) is not routinely used before the third trimester; MVP is the preferred method throughout pregnancy because it reduces false-positive diagnoses of oligohydramnios by approximately 50% without compromising detection of adverse outcomes. 1, 4
AFI measurement (summing four quadrants) becomes more standardized after 15 weeks, with progressive rise until 26 weeks gestation. 5
Using AFI instead of MVP leads to unnecessary obstetric interventions without improving perinatal outcomes. 1, 6
Clinical Context at 13-14 Weeks
At 13 weeks 6 days or less, the conceptus is termed an embryo; beginning at 11 weeks 0 days, it becomes a fetus. 3
Cardiac activity should be documented as rhythmic pulsations—avoid terms like "heartbeat" or "heart motion" since the heart is not fully formed at this stage. 3
The yolk sac should still be visible and typically measures < 6 mm; it is always located outside the amniotic cavity. 3
Common Pitfalls to Avoid
Do not diagnose oligohydramnios based solely on clinical fundal height measurements when ultrasound-derived MVP is within normal limits (≥ 2 cm). 1
Do not use AFI as the primary assessment tool at 13-14 weeks; this leads to over-diagnosis and unnecessary intervention. 1, 4
Ensure the measurement excludes umbilical cord loops and fetal/embryonic parts, which can falsely reduce the measured pocket depth. 1
If the gestational sac appears eccentrically located but is completely surrounded by endometrium, this represents a normal intrauterine pregnancy—not an ectopic or interstitial pregnancy. 3