Lecture 5
General med_2nd semester
Development of external form of the embryo
and fetus. The rule of Hasse
Uterine growth during pregnancy
Marks of the mature and full-term fetus
Multiple pregnancy: mono- and dizygotic
twins; arrangements of fetal membranes in
twins
Position, posture and presentation of the fetus
Uterine growth during pregnancy
the uterus of a nonpregnant female lies in the pelvis minor, during pregnancy it increases in size
to accommodate the growth of the fetus
the increasing uterus is to touch through the ventral wall of the abdomen
 3rd month - uterine fundus corresponds to the superior aspect of the pubic symphysis
 5th month - uterine fundus occupies the half distance between the umbilicus and pubic
symphysis
 6th month - uterine fundus is just in the level of the umbilicus
 8th month - uterine fundus lies at the half distance between the umbilicus and xiphoid
process
 9th month - uterine fundus is just in level of the xiphoid process
 10th month - uterine fundus descends and is located for about two fingers below the
xiphoid process
the increase in size
of the uterus results from
hypertrophy of preexisting
muscle cells
Estimation of the date of birth
the date of birth is calculated according to the day of fertilization or the onset
of the last normal menstrual period
in the first case, birth follows after 266 days after estimated day of
fertilization (38 weeks = 8 3/4 calendar months= 9 1/2lunar months)
in the second case, birth follows after 280 days after onset of the last
menstrual period (LMP) (40 weeks =91/4 calendar month=10 lunar month)
Marks of the mature (full-term) fetus
in the human, the pregnancy lasts 280 days or 40 lunar weeks from the 1st
day of LMP (266 days or 38 weeks after fertilization)
fetuses born ± 10 to 14 days before or after term are called mature or
full-term
if they born before 37th week - premature and born after 42 weeks postmature ones
criteria or signs of maturity of the fetus: are major and the auxiliary ones
Major marks:
length of fetus - about 50 cm,
weight of fetus - 3200 to 3500 g,
in males testes are within the scrotum, in females labia minora
are covered with labia majora
dimensions of the new-born head should be in norm
(head circumference to circumference of shoulders or chest should be 35:34)
Auxiliary marks:
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skin of the fetus is pink
only residues of fine lanugo hairs are found
hairs on head are at minimal 1 cm long
nails have grown beyond the tips of the digits
in the distal epiphysis of the femur is a distinct ossification centre
baby is plump and cries
Rule of Hasse
used for estimation of fetal age of a unknown fetus (important in
forensic medicine)
 from the 3rd to 5th month, the length of fetus is equal with the
second power of respective month (9, 16, 25 cm)
 from the 6th to 10th month, the length of fetus is equal with
product 5 x respective month (30, 35, 40, 45, 50 cm)
Dimensions of head in newborns
are transverse and longitudinal
transverse dimensions:
- bitemporal distance - 8 cm (there is a distance of two points on the
coronal suture lying each other as far as possible)
- biparietal distance - 9.5 cm (there is a distance between the centres of
both parietal tubera)
Dimensions of head in newborns
longitudinal dimensions:
- frontooccipital distance - 12 cm (there is a distance between the
centre of the forehead and external occipital protuberance), frontooccipital
circumference - 34 cm,
- distance subocciput-bregma - 9.5 cm (from bregma to the external
occipital protuberance), circumference subocciput-bregma 32 cm,
- mentooccipital distance - 13.5 cm (from the centre of the chin to the
external occipital protuberance), mentooccipital circumference 35 to 36 cm.
Multiple pregnancies: Mono- and dizygotic twins; arrangement of fetal
membranes in twins
multiple pregnancies occur in the human
labor of
twins falls on 90 pregnancies
triplets on 90 x 90 pregnancies (902)
quadruplets on 90 x 90 x 90 (903)
pregnancies
Twins may be of two categories:
dizygotic or fraternal - two zygotes
monozygotic or identical - one zygote
cca 2/3 of all twins are dizygotic
Dizygotic twins: result from fertilization of two ova by two different
spermatozoa
three possible ways of origin are supposed:
1) both ova have developed in the same follicle - fertilized simultaneously
2) the ova derive from two follicles in the same ovary
3) one ovum was developed in the left and the other in the right ovary
dizygotic twins may be of the same sex or different one
genetically, they are no more alike than brothers or sisters born at different times
dizygotic twins always have
separate fetal membranes:
two amnions
two chorions +
two placentas
chorions and placentas may be
fused in various extent
Monozygotic twins
are always of the same sex because result from fertilization of one ovum
they are genetically identical and very similar in physical appearance
an arrangement of fetal membranes in these twins depends upon the twinning time
twinning may occur in:
 immediately after the first mitosis of zygote - twinning on two-cell stage
(the zona pellucida is precociously dissolved, blastomeres then loose close contact and may
develop independently each other
each fetus has proper fetal
membranes (separate)
Monozygotic twins
 around the end of the first week in time developing of inner cell mass
(it can develop two embryonic primordia or the inner cell mass or embryoblast secondary divides
into two parts)
subsequently, two embryos develop, each in its
own amniotic sac but within one chorionic sac such twins have
two amnions
one common chorion and placenta
Monozygotic twins
 around the end of the second week (between day 13- 15) if the duplicated
primitive streak and chordomesodermal process develop
twins have common all fetal membranes
one common amnion
one common chorion and placenta
Position, posture and presentation of the fetus
(in the uterus)
Position of the fetus (situs fetus) is defined as a relation of its longitudinal axis
to the longitudinal axis of the uterus
3 positions are distinguished:
- longitudinal position - both axes run parallel - in 99,5 per cent
- transverse position - both axes are rectangle
- oblique position - axes are passing (instable position)
The longitudinal position:
by head (96,5 %) or
by breech (pelvic end of the fetus) - 3 %.
The back of the fetus is most often oriented to the left edge of the uterus
Posture of the fetus (habitus fetus) is defined as a relation of fetal body parts
to each other
may be regular and irregular
regular posture = the head is in flexion, the chin is in close contact with the chest,
upper and lower limbs are flexed in both articulations and are folded
Presentation of the fetus (praesentatio fetus) is defined as a relation of the
fetal body part to the pelvic aditus
cases that occur:
- cephalic presentation - is physiological or normal
- breech presentation - by pelvic end of the fetus - rare,
- foot or knee presentation - very rare,
- malpresentation - any abnormal presentation