ANATOMY OF THE FETAL STOMACH

• Anechoic fluid filled structure in the left upper quadrant.
• On same side as apex of the heart (Situs solitus).
• Always seen by 14 weeks (may be visible as early as 9 weeks).

• Fundus - posterior; Antrum - anterior.
  Incisural angularis
• Seen in well-distended stomach.
• Usually along lesser curve between body and antrum.
• Varying depth.

• Size:
• Varies with normal filling (fetal swallowing), emptying, gastric absorption and gastric secretion (1). There changes in normal gastric dimension changes with time (measurements made 20 mins apart may differ by 17% for longitudinal and 25% for transverse axes) (1).
• Swallowing activity has been observed as early as 16 weeks in the fetus (2). It is however minimal and episodic until 30 weeks GA (3). The volume of amniotic fluid swallowed by a normal fetus does increase with gestational age (2).
• Stomach – longitudinal diameter (Table)– Goldstein et.al. 1987
• Stomach – transverse diameter (Table) – Goldstein et.al. 1987
• Stomach – longitudinal diameter (Graph) – Goldstein et.al. 1987
• Stomach – transverse diameter (Graph) – Goldstein et.al. 1987

• Small or non visualized despite 45 minutes of scanning is abnormal.
• Enlarges linearly with gestational age.
      4 X 6 X 9 mm at 13-15 weeks.
      16 X 20 X 32 mm at 37-39 weeks.
• Enlarged or distended stomach is abnormal.

Varying appearances of normal stomach size and shape
Big normal stomach. Microgastria – exclude esophageal atresia.

REFERENCES

1. Zimmer EZ, Chao CR, Abramovich G et.al. Fetal stomach measurements: Not reproducible by the same observer. J Ultrasound Med 1992;11:663.
2. Pritchard JA. Fetal swallowing and amniotic fluid volume. Obstet Gynecol 1966;28:606.
3. McLain CR. Amniographic studies of the gastrointestinal mobility of the human fetus. Am J Obstet Gynecol 1963;86:1079.
4. Nagata S, Koyanagi T, Horimoto N et.al. Chronological development of the fetal stomach assessed using real time ultrasound. Early Hum Dev 1990;22:15.
5. Goldstein I, Reece EA, Yarkoni S et.al. Growth of the fetal stomach in normal pregnancies. Obstet Gynecol 1987;70:641.