1

Anencephaly + Neuropathology +/- Karyotyping +/- Histopathology

Nonimmunologic hydrops fetalis + Karyotyping

Other malformation +/- Histopathology

+ Karyotyping +/- Molecular studies

Crown-rump length (mm) 30 60 90 120 150 180 210 240 270 300 330 360 390

Crown-rump length (mm) 30 60 90 120 150 180 210 240 270 300 330 360 390

Figure 16.2 Placental weight at term; average weight is 500 g (range 350-600 g).

Gestational age (weeks)

Figure 16.2 Placental weight at term; average weight is 500 g (range 350-600 g).

Menstrual

Umbilical cord

age (week)

length (cm ± 1 SD)

20 to 21

32.4 ± 8.6

22 to 23

36.4 ± 9.0

24 to 25

40.1 ± 10.1

26 to 27

42.5 ± 11.3

28 to 29

45.0 ± 9.7

30 to 31

47.6 ±11.3

32 to 33

50.2 ±12.1

34 to 35

52.5 ± 11.2

36 to 37

55.6 ±12.6

38 to 39

57.4 ± 12.6

40 to 41

59.6 ±12.6

42 to 43

60.3 ± 12.7

44 to 45

60.4 ± 12.7

46 to 47

60.5 ± 13.0

Figure 16.3 Placenta cord insertion and umbilical cord length. From Naeye (1985), by permission.

Figure 16.3 Placenta cord insertion and umbilical cord length. From Naeye (1985), by permission.

(a) Mono chorionic monoamniotic placenta indicative of fertilization of one ovum by one sperm and separation into two embryonic discs 8 days or more after ovulation. About 1% of all twin pregnancies. About 7% of monozygous twin pregancies.

(c) Fused dichorionic diamniotic placenta (35^40% of all twin pregnancies) indicative of: (i) fertilization of one ovum by one sperm and early separation of the blastomere (0-3 days post-ovulation) 10% of all monozygous twin pregnancies; (ii) fertilization of two ova by two sperm and implantation in juxtaposition. 35-40% of all dizygous twin pregnancies.

(b) Monochorionic diamniotic placenta indicative of fertilization of one ovum by one sperm and separation into two embryonic discs between 3 and 8 days after ovulation. 20-30% of all twin pregnancies. 70-75% of all monozygous twin pregnancies.

(d) Separate dichorionic diamniotic placentas (35-50% of all twin pregnancies) indicative of: (i) fertilization of one ovum by one sperm, early separation of blastomeres and separate implantation sites (0-3 days post-ovulation) 15% of all monozygous twin pregnancies; (ii) fertilization of two ova by two sperm which implant at separate sites 60-65% of all dizygous twin pregnancies.

n—I—I II—I—I—I—I—I—I—I—I—I—I—I—I—I—r

Zona Pellucida

___Embryo mninn n—I—I II—I—I—I—I—I—I—I—I—I—I—I—I—I—r

Zona Pellucida

___Embryo mninn

Allantois

Primitive streak

Yolk sac

Allantois

Primitive streak

2 chorions 1 chorion

Conjoined

2 yolk

DiDi Di Mo Mo Mo sacs 1 yolk sac

2 4 6f 8 10 12 14 16 18 20 Implantation

Ovulation age (days)

Figure 16.4 Twinning, timing and membranes. From MacGillivay et al. (1975), by permission.

Ovulation

Weight

CR length

Brain

Heart

Lungs

Liver

Kidneys

Adrenals

Thymus

Spleen

Pancreas

age (days)

(g)

(mm)

(g)

(g)

(g)

(g)

(g)

(g)

(g)

(g)

(g)

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