IUGR or Intra Uterine Growth Retardation is defined as a slow rate of growth in-utero, with the fetus below the 3rd percentile for various growth measurements (e.g. weight, length, head & abdominal circumference, femur length), with pathological cause. It is not directly interchangeable with SGA (small for gestational age), which is defined as below the 10th percentile (i.e. smaller than 90% of other babies) and is non pathological in nature [1]. A low birth weight is defined as a below 2.5kg at birth, while a very low birth weight is below 1.5 kg.
Symmetrical � this type is less common, the whole body is proportionally smaller, including the size of internal organs, increasing the risk for neurological complications
Asymmetrical � �Head Sparing� the head and thus brain size remains relatively normal (to protect its development) while the rest of the body is noticeably smaller.
[2] Baby with IUGR
What are the risk factors for IUGR?
The most common risk factor for IUGR is an abnormality of the placenta [3]. One function of the placenta is to transfer essential nutrients from the maternal to the fetal circulation, such as glucose (for respiration), iron (a key component of haemoglobin), amino acids (cell division), calcium (bone development) and immunoglobulins, namely IgG (which is the most versatile and abundant, opsonises antigens).
Its other functions include the facilitation of gas exchange (oxygen to the fetus as its pulmonary circulation is not yet mature, and removal of carbon dioxide to be exhaled by the mother), removal of waste products like urea (which can also end up in the amniotic fluid) and the secretion of hormones.
It releases beta-hCG (maintains the corpus luteum), oestrogen and from 8 weeks of pregnancy, progesterone (to maintain endometrial lining), taking over from the corpus luteum. Placental function is rendered much less effective if there is incomplete trophoblastic invasion and spiral artery remodelling [4]. This is also a contributing cause of pre-eclampsia [5], which in itself is a risk factor for IUGR. Placenta praevia however, i.e. positioning of the placenta such that it obstructs the cervix is not an independent risk factor. [6]
[7] Spiral Artery Remodelling (left)
Other uteroplacental causes include multiple gestations, whereby the maternal resources are rationed between the foetuses, thus reducing the potential for growth in either one or both of them. Haemorrhages and umbilical/uterine malformations also increase the risk, as well as intrauterine infections or chromosomal abnormalities of the baby.
The last class of causes are maternal in nature. A low pre-pregnancy weight and poor nutrition is indicative of IUGR, given that the mother is essentially �eating for two�, as are: alcohol consumption (toxic to an underdeveloped fetal liver), smoking tobacco, other drugs, diabetes, hypertension, anaemia, STDs, cardiovascular disease, renal disease and pulmonary disease.
How is a baby monitored in utero?
The most reliable method for determining fetal growth antenatally is Doppler ultrasound. However, its success depends on the skill level of the operator and can often give high rates of false positives. Ultrasound can be used to detect issues such as neural tube defects, polydactyly, dwarfism, cleft lip, Down�s syndrome, multiple gestations, the child�s gender, placental position, and to see if the baby is moving around within. It is useful also to measure the umbilical vein diameter and blood flow within to determine if there is sufficient supply to the fetus. There may also be less oxygen if the baby is born at high altitude. [8]
The Symphysis-Fundal height is measured in centimetres from the mother�s pubic bone to the top of the uterus. It should be equivalent to the number of weeks of gestation elapsed within 3cm, and this is valid from week 24 (from last menstrual period). [9] One would expect the measurement to be smaller than normal for IUGR. This could indicate olighydramnios, a reduced volume of amniotic fluid, suggesting growth restriction. A diagnosis is made using ultrasound to determine the amniotic fluid index. A range of 8 to 18 inclusive is normal, thus 7 and below is a positive result. Conversely, a measurement above 18 indicates polyhydramnios, as seen with maternal diabetes, fetal renal problems and multiple births.
Chorionic villus sampling takes cells from the placenta and analyses their DNA to look for genetic and thus any potential inherited abnormalities. It is usually performed between 10 and 13 weeks gestation, either transabdominally or transcervically. One in every 50 tests however results in a miscarriage, and there is a small chance of infection and oligohydramnios. [10]
Amniocentesis is performed around 15 weeks in the second trimester and is a sample of the amniotic fluid. Its main function is to diagnose chromosome disorders, including Down�s syndrome (trisomy 21), Patau syndrome (trisomy 13), Edwards� syndrome (trisomy 18), Turner syndrome (monosomy X) and Kleinfelter�s syndrome (XXY).[11] Amniocentesis can also detect cytomegalovirus infection, haemophilia, thalassaemia , sickle cell anaemia and rhesus status of mother and child. [12]
If tests are inconclusive, then percutaneous umbilical cord blood sampling can be done (with greater risks) to sample the fetal blood.
Cardiotocography measures the fetal heart rate in utero and its relation to uterine contractions, as well as when the baby is moving inside. The relation between heart rate and movement is known as a non-stress test; a stress-test is between heart rate and contractions. A normal baby�s heart rate will increase upon movement and remain the same upon contractions. Cardiotocography can be an early indicator of hypoxia. Its continuous use has been found to reduce the incidence of neonatal seizures but not of mortality or cerebral palsy, while increasing the probability of birth by caesarean section or instrument assisted delivery. [13]
Fetal weight in the uterus can be determined from various measurements such as the head circumference, abdominal circumference and femur length. When the ratios between these are increased, then one can assume a case of IUGR is present.
Maternal blood is also checked for HIV and other potentially transferrable conditions, blood type, rhesus as mentioned before, infections, diabetes and blood pressure. The mother is also subjected to urinanalysis, a BMI check, glucose tolerance test, and history check.
What are the types of assisted delivery?
Forceps are used to grip the baby�s head to help pull the baby out while the mother pushes via her own contractions, while a Ventouse involves a suction cup that pulls on the baby�s head. Forceps deliveries are more successful but result in more pain and discomfort for the mother. Both methods leave structural abnormalities of the skull that resolve spontaneously over time.
A caesarean section (C-Section in the US) is when a baby is delivered through an incision made through the abdomen and uterus of the mother, thus bypassing the natural method of birth. Currently 1 in 4 births in the UK is done this way. It can be either pre-planned (elective) or an emergency. [14] Relative to IUGR, a caesarean or alternate early delivery will be performed post 34 weeks gestation. Before this checkpoint, the baby will continue to be monitored. A caesarean is usually performed if dangerous complications for the mother or baby arise, in cases of multiple births, placenta praevia, a history of two previous caesarean sections or if labour has stalled.
An episiotomy involves making a slit from the posterior vaginal wall into the perineum, to allow a greater diameter of birth canal for the baby to pass through. This is needed if the baby is too large, has shoulder dystocia (anterior shoulder trapped behind pubic symphysis), at risk of asphyxia, if the mother�s perineum/tissues are at risk of tearing or if the baby becomes stuck, among other reasons. Generally it quickens delivery and reduces trauma to the mother but does present risk of infection and may be painful for a while after. [15]
[15] Episiotomy Procedure
A breech birth occurs when the baby is positioned feet first upon delivery; these are most common in premature babies, such as those with IUGR. External cephalic version can then be used to rearrange the baby into the normal position with varying degrees of success. An alternative to caesarean delivery in this case could be a symphysiotomy (which is combined with an episiotomy, where the cartilage of the pubic symphysis is split in order to further open up the pelvic cavity and make delivery easier.
Oxytocin, also known as the �cuddle hormone�, is a hormone released not only during intercourse to facilitate pair bonding and build feelings of trust and connection, but is involved in a positive feedback loop for lactation and uterine contractions during childbirth; the latter is by a Ferguson reflex, where the cervical stretch receptors instigate this positive feedback. Additional oxytocin therefore, can be given to a woman to improve the delivery process. Prostaglandins induce cervical ripening which allows it to dilate more easily. [16] The mucous membranes around the cervix can be �swept� manually (which also releases prostaglandins) or broken with a small sterile hook to help induce labour.
Delivery is also �assisted� and made more tolerable for the poor mother via the use of painkillers. Nitrous Oxide and oxygen are given via mask to relieve pain, an anaesthetic or opiate agent such as lidocaine or pethidine respectively is administered locally, such as in the pudendal (S2-4) or ilioinguinal nerve, or given as a caudal epidural or in the subarachnoid space (L4-5) to remove sensation below the waist. Opiates however can suppress the baby�s respiratory drive and should be given with great care.
What is the treatment/management of IUGR?
The baby is often delivered prematurely by caesarean section. Up until 37 weeks, it may be given glucocorticosteroids (such as betamethasone) to stimulate production of surfactant in the lungs to prevent respiratory distress syndrome, the biggest killer in pre-term babies; a trained paediatric resuscitator should therefore be present at birth. Post-natally, the baby will be incubated, where factors such as temperature (as the baby has poor thermoregulation ability), humidity (for fluid balance) and oxygen will be closely monitored and regulated. Nutrients and medications will be given intravenously and ultraviolet & blue light will help with neonatal jaundice.
What short and long term complications are there for the fetus?
Short term wise, here is a greater risk of intrapartum fetal distress, hypoxic ischaemic encelopathy, stillbirth, meconium aspiration, pre-eclamptic toxaemia, pneumothorax, bacterial pneumonia and other infections, polycythemia and hyperviscosity, ruptured uterus or bleeding placenta. The newborn will have reduced glycogen and lipid stores, resulting in birth hypoglycaemia and hypothermia. In the long term the IUGR baby is at risk of cardiovascular disease (Those born weighting below 2500g are three times more likely to die of coronary heart disease), type 2 diabetes, dyslipidaemia, hypertension, autoimmune thyroid disease and neurological problems in later life. In fact there is morbidity in 20% of surviving infants. [17]
Barker�s hypothesis supports the notion that a low birth weight, caused by IUGR and thus a recalibration of metabolic and endocrine homeostasis, increases the likelihood of unwanted cardiovascular problems in the future. [18]
