Fetal Growth & Development

FETAL GROWTH AND DEVELOPMENT

Previously, methods used to determine how well the fetus was growing and maturing consisted of evaluating uterine growth and listening to fetal heart sounds. Advances in knowledge and technology have provided newer methods for assessing fetal well-being and maturity. Improved methods for assessment and diagnosis enable early intervention for improved outcome.

Stages of Growth and Development

The growth and development of the fetus is typically divided into three stages.

• Preembryonic Stage: Fertilization to 2 to 3 Weeks
• Rapid cell division and differentiation
• Develop embryonic membranes and germ layers
• Embryonic Stage: 4 to 8 Weeks' Gestation
• Most critical stage of physical development
• Organogenesis
• Fetal Stage: 9 Weeks to Birth
• Every organ system and external structure present.
• Refinement of fetus and organ function occurs.

Development by Month

First Lunar Month

• Fertilization to 2 weeks of embryonic growth.
• Implantation is complete.
• Primary chorionic villi forming.
• Embryo develops into two cell layers (trophoblast and blastocyst).
• Amniotic cavity appears.

 Second Lunar Month

• 3 to 6 weeks of embryonic growth.
• At the end of 6 weeks of growth, the embryo is approximately ½ inch (1.2 cm) long.
• Arm and leg buds are visible; arm buds are more developed with finger ridges beginning to appear.
• Rudiments of the eyes, ears, and nose appear.
• Lung buds are developing.
• Primitive intestinal tract is developing.
• Primitive cardiovascular system is functioning.
• Neural tube, which forms the brain and spinal cord, closes by the 4th week.

Third Lunar Month

• 7 to 10 weeks of growth.
• The middle of this period (9 weeks) marks the end of the embryonic period and the beginning of the fetal period.
• At the end of 10 weeks of growth, the fetus is approximately 2 ½ inches (6.3 cm) from crown to rump and weighs  ½ oz (14 g).
• Appearance of external genitalia.
• By the middle of this month, all major organ systems have formed.
• The membrane over the anus has broken down.
• The heart has formed four chambers (by 7th week).
• The fetus assumes a human appearance.
• Bone ossification begins.
• Rudimentary kidney begins to secrete urine.

Fourth Lunar Month

• 11- to 14-week-old fetus.
• At the end of 14 weeks of growth, the fetus is approximately 4 ¾ inches (12 cm) crown-rump length and 3 ¾ oz (110 g).
• Head erect; lower extremities well developed.
• Hard palate and nasal septum have fused.
• External genitalia of male and female can now be differentiated.
• Eyelids are sealed.

Fifth Lunar Month

• 15- to 18-week-old fetus.
• At the end of 18 weeks of growth, the fetus is approximately 6 ¼ inches (16 cm) crown-rump length and 11 ¼ oz (320 g).
• Ossification of fetal skeleton can be seen on x-ray.
• Ears stand out from head.
• Meconium is present in the intestinal tract.
• Fetus makes sucking motions and swallows amniotic fluid.
• Fetal movements may be felt by the mother (end of month).

Sixth Lunar Month

• 19- to 22-week-old fetus.
• At the end of 22 weeks of growth, the fetus is approximately 8 ¼ inches (21 cm) crown-rump length and 1 lb 6 ¼ oz (630 g).
• Vernix caseosa covers the skin.
• Head and body (lanugo) hair visible.
• Skin is wrinkled and red.
• Brown fat, an important site of heat production, is present in neck and sternal area.
• Nipples are apparent on the breasts.

Seventh Lunar Month

• 23- to 26-week-old fetus.
• At the end of 26 weeks of growth, the fetus is approximately 10 inches (25 cm) crown-rump length and 2 lb 3 ¼ oz (1,000 g).
• Fingernails present.
• Lean body.
• Eyes partially open; eyelashes present.
• Bronchioles are present; primitive alveoli are forming.
• Skin begins to thicken on hands and feet.
• Startle reflex present; grasp reflex is strong.

Eighth Lunar Month

• 27- to 30-week-old fetus.
• At the end of 30 weeks of growth, the fetus is approximately 11 inches (28 cm) crown-rump length and 3 lb 12 oz (1,700 g).
• Eyes open.
• Ample hair on head; lanugo begins to fade.
• Skin slightly wrinkled.
• Toenails present.
• Testes in inguinal canal, begin descent to scrotal sac.
• Surfactant coats much of the alveolar epithelium.

Ninth Lunar Month

• 31- to 34-week-old fetus.
• At the end of 34 weeks of growth, the fetus is approximately 12 ½ inches (32 cm) crown-rump length and 5 lb 8 oz (2,500 g).
• Fingernails reach fingertips.
• Skin pink and smooth.
• Testes in scrotal sac.

Tenth Lunar Month

• 35- to 38-week-old fetus; end of this month is also 40 weeks from onset of last menstrual period.
• End of 38 weeks of growth, fetus is approximately 14 ½ nches (36 cm) crown-rump length and 7 lb 8 oz (3,400 g).
• Ample subcutaneous fat.
• Lanugo almost absent.
• Toenails reach toe tips.
• Testes in scrotum.
• Vernix caseosa mainly on the back.
• Breasts are firm.