Lecture 02 HIGHLIGHTS

Foetal Period-I 3rd TO 6TH MONTH

By:

A. Prof. Dr Farooq A. Khan

PMC

Date: 11th Nov. 2017

• The Development from embryo to fetus is not abrupt, but the embryo

changes to a recognizable human being and develops all the basic outlines

of its organs and is then called a fetus.

Introduction

• Pregnancy is a period of time in which developing child resides with a

mother.

• During this time child will begin to physiologically develops the tissues,

organs and other structures needed for survival.

• Pregnancy is described in many other ways by:

• Months (0-10)

• Weeks (0-43) and by

• Trimesters.

• Most women seeks Obstetric care have at least

one ultrasound examination during their

pregnancy for one or more of the following

reasons:

USE OF ULTRASOUND EXAMINATION OF EMBRYOS

• Estimation of gestational age and number of

pregnancies and for confirmation of clinical

dating.

• Evaluation of intrauterine growth when

intrauterine growth retardation is suspected.

• Sampling of fluid.

• Suspected ectopic pregnancy.

• Possible uterine abnormalities.

• Detection of congenital anomalies.

• Current data indicates that there are no confirmed

biological effects of ultrasonography of embryos or

fetuses from the use of diagnostic ultrasound

evaluations

METHODS OF MEASURING EMBRYOS OR FOETUSES

Because embryos of the third and early fourth weeks are straight, measurements of them indicate the Greatest Length (GL).

The length of the older embryos and fetuses is usually indicated as the Crown-Rump Length (CRL) (sitting height) ( from the vertex of the skull to the midpoint between the apices of the buttocks or

METHODS OF MEASURING EMBRYOS OR FOETUSES

As the Crown-Heel Length (CHL), the measurement from the vertex of the skull to the heel (standing height).

These measurements are expressed in centimeters and are correlated with the age of the fetus in weeks or months with tables.

LENGTH OF PREGNANCY (EDD or EDC)

Length of Pregnancy (EDD) is considered to be 280 days or 40 weeks after the onset of the LNMP or more accurately, 266 days or 38 weeks after fertilization.

The common delivery date rule (Nägele's rule) for estimating the EDC is to count back 3 months from the first day of the LNMP and add a year and 7 days e.g.

First day of LNMP = January 4, 2016

Subtract 3 months = October 4, 2015.

Add a year and 7 days = October 11, 2016 = EDD

Implantation bleeding may result in miscalculation by two or more weeks.

LENGTH OF PREGNANCY (EDD or EDC) Naegele’s Rule also assumes that all women have exactly 28 day cycles and that

they ovulate on cycle day 14.

Obviously, this is not true.

There is great variation in both cycle length and ovulation timing.

There is a suggested alternative formula, Parikh’s Formula, which is a date

calculated by adding 9 months to a woman’s LMP, then adding the length of her

average cycle, then subtracting 21 days.

For example, a woman with 35 day cycles whose last period began on 1st

January would do the following calculation:

1st January + 9 months = 1st October.

1st October + 35 days = 4th November

4th November – 21 days = 14th October

This EDD is approximately one week later than EDD calculated by Naegele’s

Rule.

LENGTH OF PREGNANCY or EDD

Various measurements and external characteristics are useful for estimating fetal age.

Ultrasonographic examination and measurement of the CRL is the method of choice for estimating fetal age until the end of the first trimester because there is very little variability in fetal size during this period.

• In the second and third trimesters, several structures can

be identified and measured ultrasonographically e.g.,

BIPARIETAL DIAMETER (BPD): diameter of head between the

two parietal eminences.

HEAD CIRCUMFERENCE

ABDOMINAL CIRCUMFERENCE

FEMUR LENGTH.

FOOT LENGTH

BIPARIETAL DIAMETER (BPD)

The BPD remains the standard against

which other parameters of gestational age

assessment are compared.

The BPD should be measured as early as

possible after 13 weeks for dating.

The BPD is useful for dating a pregnancy

and in estimating intrauterine fetal weight

in weight equation.

It’s value is limited and can sometimes be

misleading in the assessment of growth in

the fetus if it is the sole measurement taken

for interpretation.

The BPD can be used to determine

gestational age with a 95% confidence of

10 to 14 days.

Femur Length(FL)

The FL is a mandatory measurement.

Apart from knowing about the longitudinal

growth of the fetus.

Measuring the FL has a very important function

of excluding dwarfism in the fetus.

The use of FL in dating is similar to the BPD, and

is not superior unless a good plane for the BPD

cannot be obtained or that the head has an

abnormal shape.

MONTHLY CHANGES

One of the most striking changes taking place during fetal life is the relative slowdown in growth of the head compared with the rest of the body.

At the beginning of the 3rd month, the head constitutes approximately half of the CRL.

By the beginning of the 5th month, the size of the head is about 1/3 of the CHL, and

At birth it is approximately 1/4 of the CHL .

Hence, with time, growth of the body accelerates and that of the head slows down.

3rd MONTH ( 9-12 weeks )

APPEARANCE:

Resembles a human being but the head is large i.e. ½ of the CRL.

The eyes are widely separated, the ears are low-set, and the eyelids are fused.

UMBILICAL HERNIA:

During 6th week, midgut herniated in the umbilical cord.

Hernia gets reduced in the 3rd month. Mid of 10th week = Prox. Umbilical Cord End of 10th week = Reduced

PRIMARY OSSIFICATION CENTRES:

They are present in long bones and skull by the end of 12th week.

9th week 11th week

3rd MONTH ( 9-12 weeks ) cont’ d

RELATIVE LENGTH OF LIMBS:

The upper limb attain their final relative length but the lower limbs are still a little shorter than their final relative length.

NAILS:

Begin to appear on digits

SEX OF FOETUS:

By 12th week, external genitalia develop to such a degree that sex can easily be identified by imaging techniques like ultrasonography

3rd MONTH ( 9-12 weeks ) cont’ d

ERYTHROPOEISIS:

At nine weeks, the liver is the major site of erythropoiesis.

By the end of the 12th week, the spleen takes over .

URINE FORMATION:

Begins during the 3rd month and urine is discharged into the amniotic fluid. 12 week

4th MONTH ( 13-16 weeks )

APPEARANCE:

Face truly human

GROWTH:

It is rapid during this period and by 16 weeks the CRL reaches 115mm.

LIMB MOVEMENTS:

Which first occur at the end of the embryonic period, become coordinated by the fourteenth week but are too slight to be felt by the mother.

These movements are visible during ultrasound examinations.

OSSIFICATION:

The ossification of the the fetal skeleton is active during this period and the bones are clearly visible in ultrasound images.

13 week

4th MONTH ( 13-16 weeks ) cont’ d

EYES:

By 16 weeks the eyes face anteriorly rather than anterolaterally but still wide apart.

In addition, slow eye movements occur by week 14.

EXTERNAL EARS:

Approaching their characteristic form and are close to their definitive position on the sides of the head.

14 weeks

5th MONTH ( 17-20 weeks )

GROWTH: Slows down during this period but the fetus

still increases its CRL to about 190 mm.

QUICKENING: Limbs reach their final relative proportions

and fetal movements - quickening – are commonly felt by the mother.

VERNIX CASEOSA: Skin is now covered with a greasy, cheeselike

material - vernix caseosa, a mixture of a fatty secretion from the fetal sebaceous glands and dead epidermal cells.

Protects the delicate fetal skin from abrasions, chapping, and hardening that could result from exposure to the amniotic fluid.

20 Weeks

190 mm

5th MONTH ( 17-20 weeks ) cont’ d

EYE BROWS AND HEAD HAIR: visible at 20 weeks.

LANUGO:

20-week fetuses are usually covered with fine hair lanugo ( DOWN or WOOLY ) hair - which helps to hold the vernix caseosa on the skin.

BROWN FAT:

Forms during this period, found at the root of the neck, posterior to the sternum, perirenal area.

It is the site of heat production, particularly in the newborn infant.

20 Weeks

5th MONTH ( 17-20 weeks ) cont’ d

UTERUS and VAGINA:

By 18 weeks the uterus is formed and canalization of the vagina has begun.

OVARIES:

By this time many primordial ovarian follicles containing oogonia have formed.

TESTES:

By 20 weeks the testes have begun to descend, but they are still located on the posterior abdominal wall, as are the ovaries in female fetuses

20 Weeks

190 mm

6th MONTH ( 21-24 weeks )

WEIGHT: Substantial weight gain. Although still somewhat lean, the fetus is better

proportioned .

SKIN: Usually wrinkled and pink to red in colour. Wrinkling is due to lack of subcutaneous fat and

redness is due to blood visible in the capillaries through translucent skin

VERNIX: Abundant

LANUGO: Darkens and cover most of the body

EYE BROWS / EYE LASHES: Well developed

6 months

6th MONTH ( 21-24 weeks ) cont’ d

RESPIRATORY SYSTEM:

By 24 weeks the secretory epithelial cells (type II pneumocytes) secrete SURFACTANT.

Although several organ systems are able to function, the respiratory and CNS are still immature.

A foetus born during 6th month or the 1st half of the 7th month has little chance of survival.

FINGERNAILS:

Present by 24 weeks.

6 months

ORGANOGENESIS

t Thank You..