Transcript (LH) is taken over by human chorionic gonadotrophin (hCG)

PREGNANCY AND LACTATION
• This chapter discusses the biochemical changes
that occur in pregnancy and how clinical
biochemistry tests can be used in the investigation
of infertility.
• If the ovum is fertilized, it may implant in the
endometrium, which has been prepared by
progesterone during the luteal phase.
The function of luteinizing hormone (LH) is taken over
by human chorionic gonadotrophin (hCG), produced
by the chorion and developing placenta.
1
Human chorionic gonadotrophin is similar in structure
and action to LH and prevents the involution of the
corpus luteum as circulating pituitary gonadotrophin
concentrations fall.
Consequently, plasma oestrogen and progesterone
concentrations continue to rise and endometrial
sloughing is prevented.
Progesterone is initially produced by the corpus
luteum of the ovary for the first 8 weeks of pregnancy,
then from implantation of the embryo the placenta
takes over progesterone synthesis.
• During pregnancy the predominant oestrogen is
oestriol produced by the placenta.
2
• Prolactin concentration gradually increases during
the first two trimesters and then rises steeply, to
about 8000 mU/L, in the third trimester.
• Prolactin, oestrogens, progesterone and (human)
placental lactogen stimulate breast development in
preparation for lactation.
High plasma oestrogen concentrations inhibit milk
secretion; lactation can start only when plasma
concentrations fall after delivery of the placenta.
Initially lactation depends on prolactin.
3
• Suckling stimulates secretion of the hormone, but,
even during lactation, plasma prolactin
concentrations fall progressively post partum and
reach non-pregnant levels after 2 or 3 months.
• Apart from the effects on the breast, the high
plasma concentration of prolactin interferes with
gonadotrophin and ovarian function and produces a
period of relative infertility.
4
Monitoring pregnancy (placental
function)
• Substances produced by the fetus or placenta
(fetoplacental unit) may be measured in maternal
plasma or urine to detect fetal abnormalities or to
monitor the progress of the pregnancy,
for example
• low urine unconjugated oestriol (E3) is associated
with poor pregnancy outcome.
5
Such sampling is relatively safe and simple, but
occasionally more invasive testing, such as of
amniotic fluid obtained by amniocentesis, may be
needed.
However, the ability to visualize the fetus using
ultrasound and the use of cardiotocography for
detecting fetal heart rate have reduced the need for
such tests.
6
Human chorionic gonadotrophin
• The secretion of hCG by the placenta reaches a
peak (rising to about 500 000 U/L) at about 13 weeks
of pregnancy and then falls.
• The fetoplacental unit then takes over hormone
production, and the secretion of both oestrogen and
progesterone rises rapidly.
• Plasma or urinary hCG concentrations, which give
positive results at 1 or 2 weeks after the first missed
menstrual period, are most commonly used to
confirm pregnancy .
7
• However, by using more sensitive immunoassay
techniques, plasma hCG may be detected soon after
implantation of the ovum and before the first missed
period.
• Measurement of plasma hCG is also useful if an
ectopic pregnancy is suspected, in conjunction with
ultrasonography, or if the patient is being treated for
infertility.
8
Serial hCG measurements may be used to assess the
progress of early pregnancy; single values are
diffi cult to interpret because of the wide reference range.
• As a rough guide, plasma concentrations should double
every 2 days in a normal pregnancy.
• Raised plasma hCG not due to pregnancy can be due
to gestational or nongestational trophoblastic neoplasia
or the menopause.
9
Human placental lactogen
• This is a peptide hormone synthesized by the placenta.
It is detectable in maternal plasma after about the
eighth week of gestation.
it has been used to assess the likelihood of threatened
miscarriage .
to monitor late pregnancy, but now is rarely used.
10
Detection of fetal abnormalities
• Some fetal abnormalities may be diagnosed by
tests carried out on maternal plasma or amniotic
fluid.
• Amniocentesis is a procedure by which amniotic
fluid is obtained through a needle inserted through
the maternal abdominal wall into the uterus and is
usually carried out after about 14 weeks’ gestation.
• The procedure carries a small risk to the fetus.
11
• Both the safety and the reliability of the procedure
can be improved if combined with ultrasound
examination in order to locate the position of the
fetus, placenta and maternal bladder.
• Analytical results may be misleading if, for example,
the specimen is contaminated with maternal or fetal
blood or maternal urine, is not fresh or is not properly
preserved.
12
Close relation between the clinician and the
laboratory staff helps to ensure the suitability of the
specimen and the speed of the assay.
Amniotic fluid is probably derived from both maternal
and fetal sources, but its value in reflecting
abnormalities arises from its intimate contact with the
fetus and from the increasing contribution of fetal
urine in later pregnancy.
13
Detection of neural tube defects
• α-Fetoprotein (AFP) is a low-molecular-weight
glycoprotein synthesized mainly in the fetal yolk sac
and liver.
Its production is almost completely repressed
in the normal adult.
It can diffuse slowly through capillary membranes and
appears in the fetal urine, and hence in the amniotic
fluid, and in maternal plasma.
14
• Severe fetal neural tube defects, such as open
spina bifida and anencephaly, are associated with
abnormally high concentrations in these fluids.
• The reason for this is not clear, but the protein may
leak from the exposed neural tube vessels.
15
• As well as neural tube defects, the causes of raised
AFP concentration in amniotic fl uid and maternal
plasma include:
• multiple pregnancy,
• serious fetal abnormalities,
• exomphalos.
• In some countries, pregnant women attending for
antenatal care are offered plasma AFP assay at
between 16 and 18 weeks’ gestation to screen for the
presence of a fetus with a neural tube defect
(although highresolution ultrasound is beginning to
replace this test).
16
The gestational age should be confirmed by
ultrasound, which should also exclude a multiple
pregnancy as a cause of high concentrations.
• Positive results should be confirmed on a fresh
sample, which, if still high and if the diagnosis has not
been confirmed by ultrasound, may be followed by
AFP estimation on amniotic fluid.
•
17
• This is a more precise diagnostic test and yields
fewer false-positive results than plasma assays if
sampling is properly performed.
• It should be reserved for subjects known to be at
risk, either because of a family history of neural
tube defects or because of the finding of a high
concentration in maternal plasma with a normal or
equivocal ultrasound scan.
18
• Amniotic fluid acetylcholinesterase assay is now
rarely used to detect certain fetal malformations,
• including neural tube defects and exomphalos.
• It gives reliable results up to about 23 weeks’
gestation.
• The interpretation of the result is less dependent on
fetal age than AFP, but is equally invalidated by
contamination with fetal or maternal blood.
• The assay is less widely available than that for AFP.
19
Detection of Down’s syndrome
• Low maternal plasma AFP and unconjugated
oestriol, and raised hCG and inhibin A
concentrations, measured between 15 and 20
weeks’ gestation, are associated with an increased
risk of the fetus having Down’s syndrome
(trisomy 21) and used as a second trimester screening
test.
This combination of tests (quadruple or Quad test) to
screen for the congenital disorder is available in
specialized laboratories.
20
Fetal nuchal translucency determined by highresolution ultrasound, along with raised pre-β-hCG
and reduced pregnancy-associated plasma protein A
(PAPP-A), are used as a first trimester (10–14 weeks’
gestation) screening test;
increased nuchal thickness is associated with
chromosomal abnormalities.
A definitive test is amniocentesis, which allows the
collection of fetal cells for karyotyping.
The
• risk of Down’s syndrome increases with maternal
age.
21
Detection of other fetal abnormalities
• Chromosomal abnormalities and some inborn
errors of metabolism may be detected by cytogenetic,
biochemical or enzymatic assays on cells cultured
from amniotic fluid or after biopsy of chorionic villi.
• These tests are performed only in special centres
and usually on individuals with a family history of a
genetic condition.
• Circulating fetal (DNA) in maternal blood may also
prove to be useful.
22
Assessment of fetomaternal blood group
incompatibility
• Rhesus or other blood group incompatibility has
effects on the fetus, which may be assessed by
measuring amniotic fluid concentrations of bilirubin
in conjunction with maternal antibody titres.
Normally bilirubin concentrations in amniotic fluid
decrease during the last half of pregnancy.
The concentrations at any stage correlate with the
severity of haemolysis.
23
The result is read off a Liley chart relating optical
density of amniotic fluid at 450 nm (an indirect
measure of bilirubin) against gestational time.
Such tests may allow the optimum time for induction
of labour or the need for intrauterine transfusion to be
assessed
24
Assessment of fetal lung maturity
• The examination of amniotic fluid has also been
used to assess pulmonary maturity.
• Immature lungs do not expand normally at birth and
may cause neonatal respiratory distress syndrome
(hyaline membrane disease), with the need for
respiratory support.
• It is therefore important to have evidence of
pulmonary maturity before labour is induced.
• At about 32 weeks’ gestation, the cells lining the
• fetal alveolar walls start to synthesize a surfacetensionlowering complex
25
• (surfactant), 90 per cent of which is the
phospholipid lecithin, which contains palmitic acid.
• Surfactant is probably washed from, or secreted by,
the alveolar walls into the surrounding amniotic
fluid, inwhich both lecithin and palmitic acid
concentrations steadily increase.
• The concentration of lecithin, relative to another
lipid, sphingomyelin, which remains constant
in amniotic fluid, can be measured.
26
A rise in the lecithin to sphingomyelin ratio may help
determine pulmonary maturity, and a ratio less than 2
implies immaturity.
This invasive test is rarely indicated now as steroids,
which induce surfactant synthesis, are sometimes
given to patients who have premature rupture of the
membranes.
27
Maternal biochemical changes in
pregnancy
• Weight gain of about 12 kg occurs due to increased
maternal fluid retention, increased maternal fat stores
and also the products of conception, including the
• fetus, placenta and amniotic fluid.
• Many plasma constituents are influenced by sex
hormones. For example, the reference ranges of
plasma urate and iron differ in males and females
after puberty.
28
• Therefore it is not surprising to find that during
pregnancy the very high circulating concentrations of
oestrogens and progesterone alter the concentrations
of many substances in plasma (Table 10.1).
• The plasma concentrations of many specifi c carrier
• proteins increase during pregnancy, accompanied
by a proportional increase of the substance bound
to them, without any change in the unbound free
fraction.
29
• Because the protein-bound fraction is a transport
form and because, in all cases, it is the free
substance that is physiologically active, this rise in
concentration is of importance in the interpretation
of the results of such assays as those of plasma
thyroxine.
• Other changes in maternal plasma are due to
progressive haemodilution by fluid retained during
pregnancy.
This is maximal at about the thirtieth week and the
effects are most evident in reduced concentrations of
albumin, and of calcium, which is bound to albumin.
30
These changes are more marked in pre-eclamptic
toxaemia, in which fluid retention may be greater than
normal.
The glomerular filtration rate (GFR) increases and
creatinine clearance can be over 140 mL/min by about
28 weeks.
There is a reduced renal threshold for glucose and
increased excretion of urate and some amino acids.
• There is a mild increase in ventilation rate.
Oxygen consumption is increased, but PO2 remains
fairly constant despite a small decrease in PCO2.
There is increased fasting glucose utilization, and
therefore fasting glucose concentration is lower.
31
• Renal glycosuria is common in pregnancy and
sometimes in individuals taking oral contraceptives.
• The GFR increases by about 50 per cent during
pregnancy, resulting in a reduced plasma creatinine.
• Glycosuria may partly be due to an increased
glucose load in normal tubules.
positive protein and purine balance during the growth
of the fetus and the increase in GFR
that occurs during pregnancy result in lowered
maternal plasma urea and urate concentrations.
32
• Plasma alkaline phosphatase activity rises in some
women during the last 3 months of pregnancy due
to the presence of the placental isoenzyme and
should not be misinterpreted .
• Placental alkaline phosphatase does not cross the
placenta and therefore it is not present in
the plasma of the newborn infant.
33
34
35
Delivery
• During delivery, blood gases and lactate can be
measured in fetal blood to monitor for hypoxia.
• Capillary blood samples may be collected from the
fetal scalp during delivery.
• Transcutaneous oxygen electrodes can determine
fetal PO2.
36
Hypertension in pregnancy and
pre-eclampsia
• Pregnancy-induced hypertension or pre-eclampsia
is associated with convulsions (as occurs in
eclampsia), oedema, impaired renal function,
proteinuria and maternal death as well as with
placental insufficiency and intrauterine fetal growth
retardation.
• Pre-eclampsia is defined as a blood pressure taken
• on two occasions, at least 6 h apart, of 140/90
mmHg or greater (after 20 weeks’ gestation) in a
woman with previously normal blood pressure and
who has proteinuria (defined as 300 mg protein in
24-h urine collection).
37
• Plasma urate may rise in pre-eclampsia and is
predictive of maternal complications.
• Detection and follow-up of trophoblastic
• tumours
• Trophoblastic tumours (hydatidiform mole,
choriocarcinoma), which may follow abnormal
pregnancy or a miscarriage, and some teratomas
secrete hCG, which can be estimated in plasma or
urine by sensitive tests allowing early detection and
treatment of recurrence.
38
However, these tests will not necessarily differentiate
pregnancy or retained products of conception from
recurrence of a tumour, because plasma hCG
concentrations rise in both situations.
In monitoring trophoblastic tumours it is important to
monitor plasma hCG down to undetectable levels.
39
INFERTILITY
• Infertility can be defined as primary when
conception has never occurred despite at least 1
year of unprotected coitus, and secondary when
there has been a previous pregnancy, either
successful or not.
• Investigation earlier than at 1 year may be
appropriate if the woman is more than 35 years old
or where pregnancy is associated with other risks.
• In cases of infertility, both partners should be
investigated.
40
The history should include coital frequency and
success, serious illnesses, use of alcohol
and drugs, and sexually transmitted diseases.
• Female
Examination should include looking for anorexia
nervosa, hirsutism, virilism, galactorrhoea and
ambiguous genitalia.
A history should also be taken for medications and
drugs .
41
Investigations
• A woman may be infertile despite having a clinically
normal menstrual cycle (about 95 per cent of such
cycles are ovulatory).
Thus, even if the cycle seems to be regular, it is
important to determine whether ovulation is occurring
and if luteal development is normal.
• Anovulatory infertility is probably the most common
form of female infertility and is associated with
• oligomenorrhoea or amenorrhoea.
42
•
•
•
•
If the patient is menstruating regularly, measure
plasma progesterone concentration during the
luteal phase on day 21 of the cycle.
A normal plasma concentration is strong evidence
that the patient has ovulated.
• A low plasma concentration of < 30 nmol/L
suggests either ovulatory failure orimpaired luteal
function.
• This investigation should be repeated on more than
one occasion.
•
43
• The most common cause of a low progesterone
concentration (< 30 nmol/L) is inaccurate sample
timing, although, if authentic, it suggests lack of
ovulation.
• However, a plasma progesterone concentration of
more than 100 nmol/L suggests pregnancy.
• Follicular development and ovulation may be
• monitored by ovarian ultrasound examination.
• Polycystic ovary syndrome should be excluded
• Plasma follicle-stimulating hormone (FSH), LH,
oestrogen and testosterone concentrations are
useful, as is the exclusion of thyroid disease.
44
• If there is primary amenorrhoea, consider
karyotyping the patient, for example Turner’s
syndrome (45,XO).
• Sometimes histological examination of an
endometrial biopsy specimen or the appearance of
cervical mucus can indicate whether luteal function
is normal.
45
An oral progestogen challenge can be used: a
withdrawal bleed 5–7 days later implies adequate
endometrial oestrogen, whereas failure to bleed
despite oestrogen treatment implies uterine disease.
• Hyperprolactinaemia should be excluded by
checking the plasma prolactin concentration.
• Do the plasma FSH, LH and oestrogen results
suggest hypergonadotrophic hypogonadism or
• hypogonadotrophic hypogonadism?
46
• In the presence of amenorrhoea, a plasma FSH of
more than 40 U/L is suggestive of ovarian failure.
• Low concentrations of plasma gonadotrophins may
necessitate a gonadotrophin-releasing hormone
(GnRH) test to look for pituitary or hypothalamic
disease .
• Anti-Müllerian hormone (AMH) is released by
granulosa cells of the ovarian follicle and low serum
concentrations suggest poor ovarian ‘reserve’ (the
size of the ovarian ovum supply).
47
Serum AMH may, thus, have a place in the
investigation of infertility.
• Male
• Systemic illness, for example cystic fibrosis,
thyroid disease, gynaecomastia, eunuchoid
appearance and ambiguous genitalia, should be
excluded and any history of mumps, drugs and
medications should be obtained.
• Investigations
• Semen analysis: the volume should be at least 2
mL.
48
• There should be more than 20× 10 9/L spermatozoa,
more than 50 per cent being motile at 4 h post
ejaculation and more than 30 per cent normal
morphology.
A post-coital test is useful so that cervical mucus can
be examined for the presence of spermatozoa and
their activity.
Sperm antibodies may exist.
• Plasma testosterone, LH and FSH concentrations
should be measured.
• –
49
• Raised plasma FSH and LH concentrations with a
low testosterone concentration
(hypergonadotrophic hypogonadism) indicate
a testicular problem such as Leydig cell failure.
• Low plasma FSH and LH and testosterone
concentrations suggest pituitary or hypothalamic
disease (hypogonadotrophic hypogonadism).
• In the case of the latter, a GnRH test may be
required .
50
• A raised plasma FSH concentration in comparison
with LH may indicate seminiferous tubular failure,
irrespective of the plasma testosterone
concentration.
• There is usually azoospermia or oligospermia.
Oligospermia with a low plasma FSH concentration
suggests pituitary or hypothalamic disease.
• If there is evidence of feminization, karyotype
should be considered.
51
• This should also be considered if azoospermia is
present, for example Klinefelter’s syndrome
(47,XXY).
• Plasma prolactin should be measured and
• hyperprolactinaemia and thyroid disease excluded
Defects of the male reproductive tract may also be
found and necessitate a urology opinion.
An hCG stimulation test may be indicated if absence
of testes is suspected or to assess Leydig cell reserve
•
52
• Some tumours can release b-hCG or oestrogens
and may induce features of feminization.
• These can be assayed in plasma if the cause of
infertility is unclear.
• Sometimes, despite both partners being
investigated, no cause for the infertility can be
found. Some couples decide to try in vitro
fertilization
53
SOME DRUG EFFECTS ON THE HYPOTHALAMIC–PITUITARY–
GONADAL AXIS
• The combined oral contraceptive pills contain
synthetic estrogens and progestogens and
suppress pituitary gonadotrophin secretion and
thus inhibit ovulation.
• Withdrawal mimics involution of the corpus luteum
and results in menstrual bleeding.
• Progesterone or progestin only (mini) pills may
inhibit ovulation and also thicken cervical mucus,
thereby inhibiting sperm penetration.
54
• Clomiphene blocks oestrogen receptors in the
hypothalamus and so prevents negative feedback.
It may stimulate gonadotrophin release, even when
circulating oestrogen concentrations are high.
Clomiphene may be used to induce ovulation in
patients with amenorrhoea or infertility.
Gonadotrophin treatment may be used if clomiphene
fails to induce ovulation.
55
This therapy may cause dangerous follicular
enlargement due to hyperstimulation, or may
stimulate many follicles and so cause multiple
pregnancy.
Treatment must therefore be monitored either by
frequent plasma oestradiol estimations (which would
be expected to be very high) or by ovarian ultrasound
examination.
• Ovulation may be assessed by demonstrating rising
plasma progesterone concentrations or by
ultrasound.
56
• Gonadotrophins may also be used to stimulate the
production of enough oocytes to enable them to be
‘harvested’ for in vitro fertilization or gamete
intrafallopian transfer.
• Gonadotrophin-releasing hormone treatment
can be used for patients with infertility secondary
to hypogonadotrophic hypogonadism.
It is given subcutaneously in pulses, such as every 90
min, using a portable syringe pump.
57
Bromocriptine may reduce high plasma prolactin
concentrations, after which menstruation may resume
and fertility may be restored.
58