MILESTONES OF FETAL GROWTH AND DEVELOPMENT Flashcards
PERIOD OF ORGANOGENESIS MOST CRITICAL
FIRST TRIMESTER
● Length: 0.75–1 cm
● Weight: 400 mg
● The spinal cord is formed and fused at the
midpoint.
● Lateral wings that will form the body are folded forward to fuse at the midline.
● The head folds forward and becomes prominent, representing about one-third of the entire structure.
● The back is bent so that the head almost touches the tip of the tail.
● The rudimentary heart appears as a prominent bulge on the anterior surface.
● Arms and legs are budlike structures.
● Rudimentary eyes, ears, and nose are discernible.
End of 4th Gestational Week (4th week, 1st Month)
● Length: 2.5 cm (1 in)
● Weight: 20 g
● Organogenesis is complete.
● The heart, with a septum and valves, is beating
rhythmically.
● Facial features are definitely discernible.
● Arms and legs have developed.
● External genitalia are forming, but sex is not yet
distinguishable by simple observation.
● The primitive tail is regressing.
● The abdomen bulges forward because the fetal
intestine is growing so rapidly.
● An ultrasound shows a gestational sac,
diagnostic of pregnancy (Fig. 9.8).
End of 8th Gestational Week (8th week, 2nd month)
● Length: 7–8 cm
● Weight: 45 g
● Nail beds are forming on fingers and toes.
● Spontaneous movements are possible, although
they are usually too faint to be felt by the mother. ● Some reflexes, such as the Babinski reflex, are
present.
● Bone ossification centers begin to form. ● Tooth buds are present.
● Sex is distinguishable by outward
appearance.
● Urine secretion begins but may not yet be evident in amniotic fluid.
● The heartbeat is audible through Doppler technology.
End of 12th Gestational Week (First Trimester)
FOCUS: LENGTH OF FETUS
SECOND TRIMESTER
● Length: 10–17 cm
● Weight: 55–120 g
● Fetal heart sounds are audible by an ordinary
stethoscope.
● Lanugo is well formed
● Liver and pancreas are functioning.
● Fetus actively swallows amniotic fluid,
demonstrating an intact but uncoordinated swallowing reflex; urine is present in amniotic fluid.
● Sex can be determined by ultrasound.
End of 16th Gestational Week
● Length: 25 cm
● Weight: 223 g
● Spontaneous fetal movements can be sensed by
the mother.
● Antibody production is possible.
● The hair forms on the head, extending to include eyebrows.
● Meconium is present in the upper intestine.
● Brown fat, a special fat that will aid in
temperature regulation at birth, begins to be formed behind the kidneys, sternum, and posterior neck.
● Vernix caseosa begins to form and cover the skin.
● Passive antibody transfer from mother to fetus begins.
● Definite sleeping and activity patterns are distinguishable (the fetus has developed biorhythms that will guide sleep/wake patterns throughout life).
End of 20th Gestational Week
● Length: 28–36 cm
● Weight: 550 g
● Meconium is present as far as the rectum
● Active production of lung surfactant begins.
● Eyebrows and eyelashes become well defined.
● Eyelids, previously fused since the 12th week,
now open.
● Pupils are capable of reacting to light.
● When fetuses reach XX weeks, or 601 g, they
have achieved a practical low-end age of viability (earliest age at which fetuses could survive if born at that time), if they are cared for after birth in a modern intensive care facility.
● Hearing can be demonstrated by response to sudden sound.
End of 24th Gestational Week
Period of Most Rapid Growth FOCUS: Weight of Fetus
THIRD TRIMESTER
● Length: 35–38 cm
● Weight: 1200 g
● Lung alveoli begin to mature, and surfactant can be demonstrated in amniotic fluid.
● Testes begin to descend into the scrotal sac from the lower abdominal cavity.
● The blood vessels of the retina are formed but thin and extremely susceptible to damage from high oxygen concentrations (an important consideration when caring for preterm infants who need oxygen).
End of 28th Gestational Week
● Length: 38–43 cm
● Weight: 1600 g
● Subcutaneous fat begins to be deposited (the
former stringy, “little old man” appearance is
● lost)
● Fetus responds by movement to sounds outside the mother’s body.
● Active Moro reflex is present.
● Iron stores, which provide iron for the time during
which the neonate will ingest only milk after
● birth, are beginning to be developed.
● Fingernails grow to reach the end of fingertips.
End of 32nd Gestational Week
● Length: 42–48 cm
● Weight: 1800–2700 g (5–6 lb)
● Body stores of glycogen, iron, carbohydrate, and calcium are deposited.
● Additional amounts of subcutaneous fat are deposited.
● Sole of the foot has only one or two crisscross creases, compared with the full crisscross pattern that will be evident at term.
● Amount of lanugo begins to diminish.
● Most babies turn into a vertex (head down)
presentation during this month.
End of 36th Gestational Week
● Length: 48–52 cm (crown to rump, 35–37 cm) ● Weight: 3000 g (7–7.5 lb)
● Fetus kicks actively, hard enough to cause the
mother considerable discomfort.
● Fetal hemoglobin begins its conversion to adult
hemoglobin. The conversion is so rapid that at birth, about 20% of hemoglobin will be adult in character.
● Vernix caseosa is fully formed.
● Fingernails extend over the fingertips.
● Creases on the soles of the feet cover at least
two thirds of the surface
End of 40th Gestational Week (Third Trimester)
The spinal cord is formed and fused at the
midpoint.
4th
The rudimentary heart appears as a prominent
4th
Organogenesis is complete.
8th
The heart, with a septum and valves, is beating rhythmically.
8th
External genitalia are forming, but sex is not yet distinguishable by simple observation.
8th
An ultrasound shows a gestational sac,
diagnostic of pregnancy
8th
Nail beds are forming on fingers and toes.
12th
Sex is distinguishable by outward
appearance
12th
Spontaneous movements are possible, although they are usually too faint to be felt by the mother.
● Some reflexes, such as the Babinski reflex, are present.
12th
Fetal heart sounds are audible by an ordinary stethoscope.
16th
Lanugo is well formed
16th
Fetus actively swallows amniotic fluid,
demonstrating an intact but uncoordinated swallowing reflex; urine is present in amniotic fluid.
16th
Sex can be determined by ultrasound.
16th
Spontaneous fetal movements can be sensed by the mother
20th
Vernix caseosa begins to form and cover the skin.
20th
Eyebrows and eyelashes become well defined.
24th
Pupils are capable of reacting to light.
24th
Lung alveoli begin to mature, and surfactant can be demonstrated in amniotic fluid.
28th
Subcutaneous fat begins to be deposited (the
former stringy, “little old man” appearance is
● lost)
32nd
Active Moro reflex is present.
32nd
Body stores of glycogen, iron, carbohydrate, and calcium are deposited.
36th
Fetus kicks actively, hard enough to cause the mother considerable discomfort.
40th
