Age determination of Fetus

The lack of cartilage and the easy foldability (lack of recoil) as shown in the picture above are evident in the ear of this premature infant at 26 weeks.

• Cartilaginous development proceeds in an orderly manner during gestation and can be assessed by examination of the external ear. 
• Although the normal incurving of the upper pinnae begins at 33 to 34 weeks and is complete at term, it is more reliable to assess the extent of cartilage in the pinnae by feeling its edge and folding the ear. 
• Until approximately 32 weeks, there is only minimal recoil of a folded ear, but by term there is instant recoil.

Prominence of the labia minora in a premature female infant as shown in the picture above represents the gestational age of aprox 28 weeks.

• The appearance of the genitalia can be used to assess gestational age. 
• In a boy the testes descend into the scrotum during the last month of gestation, but they are often palpable in the inguinal canal by 28 to 30 weeks. 
• The appearance of rugae on the scrotum parallels testicular migration, appearing first on the anterior scrotum at 36 weeks and covering the entire scrotal sac by 40 weeks. 
• Absence of testicular descent alters the appearance of the scrotum at term. 
• Clearly, congenital cryptorchidism complicates this evaluation. 
• In a girl the labia majora tend to be overshadowed by the clitoris and labia minora until 34 to 36 weeks.
• In cases of fetal malnutrition, lack of subcutaneous fat, which should normally be present in the latter part of gestation, can interfere with the assessment of the female genitalia.

Ans. c. 6 weeks

Rule of Hasse

• Rule of Hasse is used to determine the age of fetus from crown to heel length in cm.
• During first five months, Length in cm = (Age in months)2
• After age of >5 months, Age in months = (Length in cm)/5
• so here Rule of Haase: During the first five months of pregnancy the square root of the length gives the approx. age of the fetus in months. So under root of 2 = 1.414 months = 1.414×30 and then divided by 7 = 42/7= 6 weeks 

Age of the Fetus

End of first month

• Length 1 cm, weight two and half gram
• Eyes are seen as two dark spots and mouth as a cleft

End of second month

• Length 4 cm, weight 10 gms
• Hands and feet are webbed°
• Anus is seen as a dark spot

Age of the Fetus

End of third month

• Length 9 cm, Weight 30 gms
• Eyes are closed°, pupillary membrane appears
• Nails appear and neck is formed

End of fourth month

• Length 16 cm, weight 120 gms°
• Sex can be recognized

End of fifth month

• Length 25 cm, weight 400 gms
• Nails are distinct and soft°
• Light hairs appear on head°

End of sixth month

• Length 30 cm, weight 700 gms
• Eyebrow and eyelashes appear°
• Subcutaneous fat begins to be deposited°
• Testes are seen close to kidney

End of seventh month

• Length 35 cm, weight 900-1200 gms
• Nails are thick
• Eyelids open and pupillary membrane disappears°
• Testes found at external inguinal ring°

End of eighth month

• Length 40 cm, weight one and half to two kg
• Nails reach the tips of fingers°
• Left testes in scrotum°

End of ninth month

• Length 45 cm, weight two and half to three kg
• Scalp hair is dark and 4 cm long°
• Scrotum is wrinkled and contains both testes°

End of tenth month

• Length 50-53 cm, weight 2.5-5 kg
• The nails project beyond the end of fingers but reach only the tip of the toes

Ans. is ‘a’ i.e., 3^rd month