Fetal Qrowth and Assessment of Gestational

The normal term infant has completed a gestation of >37 weeks and has a birth weight > 2500 g. Accurate dating of pregnancy is important in evaluating the abnormally grown infant at birth. There are two different populations of low birthweight infants, those who are 1) born premature in gestation (i.e, at < 37 weeks); or 2) small for gestational age (SGA). Infants are SGA for one of two reasons: 1) a normal intrauterine environment but abnormal development due to fetal factors (i.e., chromosomal abnormalities); or 2) an abnormal uterine environment (i.e., maternal toxemia, heart disease, etc.) leading to abnormal growth.

Many criteria have been used to estimate gestational age. Obstetrical factors employed to determine age include date of last menstrual period, auscultation of fetal heart tones (audible by Doppler at 10 weeks, and stethoscope at 20 weeks), quickening (first maternal perception of fetal movement usually occurring at 18 to 20 weeks), and fundal height (used to estimate fetal size during the first trimester ). Ultrasonography with first trimester measurements of crown-rump length accurately estimates gestation ± 3 days. Up to 30 weeks gestation, measurements of the fetal biparietal diameter, femur length, and abdominal circumference are a reliable index of fetal size (body weight) and gestational age, but afterwards may be quite variable. Physical examination may also be used in assessing gestational age. Gestational age only indirectly measures maturity, and other measurements are needed to determine organ-specific maturity (e.g., amniotic fluid lac-tase/sucrase ratio > 2 for fetal lung maturity).

6.1B

6 months 28 weeks

62 months 30 weeks

7 months 32 weeks

7i months 34 weeks

8 months 36 weeks

82 months 38 weeks

9 months 40 weeks

1.Posture

Completely Beginning of hypotonic flexion of thigh at hip

Stronger flexion

Frog-like attitude

Flexion of the four limbs

Hypertonic

Very hypertonic

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3.PopJftaÜ angle

4150'

4

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) 100°

2100°

> 80°

4.[E0rEsll^i0m angjfeoff foott

40-50°

40-50°

C^TV

Full term ct^r*

S/S^raff' sign

'Scaf sign complete with no resistance

'Scarf sign more limited

Elbow slightly passes midline

Elbow almost reaches midline

6.R^urnfto fftwcorn off forearmi

Upper limbs very hypotonic lying in extension

Flexion of forearms begins to appear, but very weak

Strong 'return to flexion.' Flexion tone inhibited if forearm maintained 30 seconds in extension

Strong 'return to flexion.' Forearm returns very promptly to flexion after being extended for 30 seconds

Passive tone. Increase of tone with maturity illustrated by means of six clinical tests. (From Amiel-Tison, C.: Arch. Dis. Child.,43:89,1968.)

Figure 6.1A & B. Many scoring systems have been devised to assess by exam the gestational age of infants at birth. The originals are shown here in figures A & B, published by Amiel-Tison. The Dubowitz examination is one of the most complete systems, combining the general physical examination performed in the first hours of life with the neurologic evaluation carried out when the infant is at least 24 hours old. The Ballard Method abbreviates the Dubowitz scoring system and uses only 12 physical and neurologic criteria. Statistically, however, the Ballard is as accurate in assessing gestation age (± 2 weeks) as more thorough examinations and is most useful in the busy clinical setting.

Dubowitz Neurological Exam

Active tone. Increase of tone with maturity illustrated by means of four tests of righting reactions. (From Amiel-Tison, C.: In Gluck, L. (ed.), Modern Perinatal Medicine, Chicago, Year book Medical Publishers, 1974, p. 347.)

Figure 6.2. A prenatal ultrasound examination showing a view of a foot. Foot length on prenatal ultrasound has been shown to correlate well with gestational age.

Figure 6.2. A prenatal ultrasound examination showing a view of a foot. Foot length on prenatal ultrasound has been shown to correlate well with gestational age.

Foot Length And Gestational Age

Figure 6.3. Graphic representation of the correlation between fetal foot length and gestational age. (Mercer et al. Scatter plots of ultrasonic feetus. gestational age. AM J Obstet Gynecol 1987; 156:350 Mosby Year Book, used with permission)

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Figure 6.4. The premature infant has a large head in relation to body size and the eyes are protruding due to disproportion between the size of the eyeballs and the orbital cavity. The skin is red to pink, shiny due to edema, transparent with highly visible arterioles and venules, and is covered by lanugo. Subcutaneous tissue is poorly developed. Scalp hair is sparse and straight. Vernix is not formed and no nipples or areolae are seen. Note that the infant lies flat on the bed, in a frog-leg position with shoulders, elbows, and knees all touching the mattress. The head is to one side or other, not in line with the trunk.

Lanugo Newborns Postmature Infant

Figure 6.5. The postmature infant appears long and skinny due to decreased subcutaneous fat stores with advancing gestation near term. The skull is hard because the sutures have started to fuse. Note the wizened facies and alert expression typical of the post-term baby. These infants tend to be wakeful and have desquamation of the skin. The hands are like a washerwomen's, dry and wrinkled, with long fingernails. Meconium staining may be seen on the umbilical cord and fingernails more commonly in the post-term infants.

Postmature Infant Dry Skin

Figure 6.6. When a fetus is undergrown due to intrauterine dysfunction, the sequence begins with loss of fat and muscle mass as noted in this growth-retarded infant. This is followed by loss of mass of less essential organs (liver, thymus, spleen, adrenals), loss of mass of more essential organs (heart), and finally loss of brain mass. If head circumference is compromised, it indicates that malnutrition must have been very severe, and it carries a poor prognosis.

Figure 6.5. The postmature infant appears long and skinny due to decreased subcutaneous fat stores with advancing gestation near term. The skull is hard because the sutures have started to fuse. Note the wizened facies and alert expression typical of the post-term baby. These infants tend to be wakeful and have desquamation of the skin. The hands are like a washerwomen's, dry and wrinkled, with long fingernails. Meconium staining may be seen on the umbilical cord and fingernails more commonly in the post-term infants.

Figure 6.6. When a fetus is undergrown due to intrauterine dysfunction, the sequence begins with loss of fat and muscle mass as noted in this growth-retarded infant. This is followed by loss of mass of less essential organs (liver, thymus, spleen, adrenals), loss of mass of more essential organs (heart), and finally loss of brain mass. If head circumference is compromised, it indicates that malnutrition must have been very severe, and it carries a poor prognosis.

Small For Gestational Age Newborns

Figure 6.7. Two systems are useful clinically to determine gestational age by examination of the eye. First, examination of die anterior eye for the presence of the tunica vasculosa lentis, apparent generally from 27 to 34 weeks. Note in this composite figure the tunica vasculosa lentis Grade IV at 27 to 28 weeks completely covers the anterior surface of the lens and then gradually decreases to Grade I by 33 to 34 weeks when only peripheral remnants of the vessels are visible on the anterior surface of the lens.

Figure 6.7. Two systems are useful clinically to determine gestational age by examination of the eye. First, examination of die anterior eye for the presence of the tunica vasculosa lentis, apparent generally from 27 to 34 weeks. Note in this composite figure the tunica vasculosa lentis Grade IV at 27 to 28 weeks completely covers the anterior surface of the lens and then gradually decreases to Grade I by 33 to 34 weeks when only peripheral remnants of the vessels are visible on the anterior surface of the lens.

Figure 6.8. The second system used to determine gestational age involves examination of the fundus to assess macular development from 34 weeks to term. This composite figure shows Stage I - dark red pigmentation appearing, 34 to 35 weeks gestation; Stage II - the annular reflex is partially evident, 36 weeks gestation; Stage III - the complete annular reflex is present, 37 weeks gestation; Stage IV - the foveolar pit can be seen, 38 weeks gestation.

Assessing Gestation Ear Cartilage

Figure 6.9. Because calcium is preferentially deposited in die last few weeks before birth, the stiffness of the baby's ear cartilage provides another test of maturity. In premature infants, the ear cartilage is deficient and the soft pinna does not spring back. On release it remains crumpled against the side of the head. At term the cartilage is more rigid similar to the adult ear.

Figure 6.9. Because calcium is preferentially deposited in die last few weeks before birth, the stiffness of the baby's ear cartilage provides another test of maturity. In premature infants, the ear cartilage is deficient and the soft pinna does not spring back. On release it remains crumpled against the side of the head. At term the cartilage is more rigid similar to the adult ear.

Fetal Remains

Figure 6.10. The presence of teeth seen by radiography in the jaw is a relatively accurate method of assessing gestational age. In the figure on the top left, incisors and cuspids have appeared but no molars, indicating a gestational age of less than 33 weeks. In the top right is shown the appearance of incisors and first deciduous molars consistent with 33 to 37 weeks gestation. On the bottom, the second deciduous molar and follicle of first permanent molar are present, indicating a gestation of greater than 37 weeks. This method is not useful in assessing infants with anhydrotic ectodermal dysplasia who have adentia.

Assessment Fetal MaturityNewborn Lanugo

Figure 6.11. Hair, particularly on the head, is a reliable marker of maturity. Premature hair is fuzzy and the hair ends tend to clump together. In the term infant the hairs are distinct, coarse and silky. Lanugo is absent prior to 20 to 22 weeks gestation, but by 30 to 32 weeks becomes diffuse over the body. By term, lanugo has mostly disappeared. There are marked racial differences among babies with respect to lanugo characteristics. Hispanic infants, in general, have considerably more body hair persisting to term and black infants often have less than average lanugo.

Figure 6.11. Hair, particularly on the head, is a reliable marker of maturity. Premature hair is fuzzy and the hair ends tend to clump together. In the term infant the hairs are distinct, coarse and silky. Lanugo is absent prior to 20 to 22 weeks gestation, but by 30 to 32 weeks becomes diffuse over the body. By term, lanugo has mostly disappeared. There are marked racial differences among babies with respect to lanugo characteristics. Hispanic infants, in general, have considerably more body hair persisting to term and black infants often have less than average lanugo.

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Responses

  • petra
    What would gestational age be of a baby who lies in frog position?
    4 years ago

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