Lecture 5Lecture 5 General med_2nd General med_2nd semestersemester

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 pregnancythe 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 lastmenstrual 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-termif 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:

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 pregnanciestriplets 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

DizygoticDizygotic twinstwins: : result from fertilization of two ova by two differentspermatozoathree possible ways of origin are supposed:

1) both ova have developed in the same follicle - fertilized simultaneously2) 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 onegenetically, they are no more alike than brothers or sisters born at different times

dizygotic twins always have separate fetal membranes:two amnionstwo chorions +two placentas

chorions and placentas may befused 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 appearancean 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 maydevelop 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 amnionone 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