When the uterus is large or small for dates.... Max Brinsmead MB BS PhD May 2015

When the uterus is LFD or SFD you first need to know… What is normal SFH = Weeks of gestation is valid only between 20 and 30 weeks Thereafter the mean runs off to 37 cm at 40 weeks This should be validated in each population And the 95% confidence limits are not less than +/- 3 cm

When the uterus is LFD or SFD you also need to know DATES accurately… Menstrual history is unreliable when… The patient is uncertain She has a good reason to tell lies Cycles are irregular Ovulation was delayed >14 days by Miscarriage Breast feeding Hormonal contraception Quickening is unreliable when… The placenta is on the anterior uterine wall The patient is obese There is something wrong with the fetus or fluid Ultrasound is unreliable when… It is done by a non expert or with poor equipment It is done late in pregnancy There is something wrong with the fetus e.g. microcephaly

If the uterus is LFD think of… Wrong dates Hydatidiform mole Multiple pregnancy Many small parts Three poles Lots of fluid and difficult to feel the baby Polyhydramnios Uterus lifted up by Previous CS Tumours e.g. Fibroids, Ovarian cyst A Large Baby

If the uterus is LFD then… Ultrasound is useful because it readily diagnoses: Hydatidiform mole Multiple pregnancy Polyhydramnios Fibroids and tumours But ultrasound is poor at: Diagnosing fetal abnormalities Estimating fetal weight If there is a large baby: Check for maternal diabetes But macrosomia more commonly due to maternal obesity +/- Excessive weight gain in pregnancy

If there is fetal macrosomia then… There is a risk of intrauterine death If the mother is diabetic And it is poorly controlled There may be birth difficulties Cephalopelvic disproportion Shoulder dystocia Maternal birth injury and PPH Vaginal breech birth may not be wise There may be neonatal problems From hypoglycaemia From birth injuries

Management of suspected fetal macrosomia… Exclude maternal diabetes or… Control maternal blood sugars before and during birth if diabetic Refer to a place where expert assistance is available Consider induction of labour but only when it is safe to do so Watch progress in labour and prepare for complications Have someone expert standby for the delivery

If the uterus is SFD think of… Wrong dates Oligohydramnios Premature rupture of membranes Abnormality of the fetal renal tract Intrauterine growth retardation (IUGR) Intra uterine growth retardation There are two major categories Symmetrical = head, trunk and body reduced proportionaely Asymmetrical = head-sparing growth restriction

Causes of Symmetrical IUGR Constitutional smallness Consider maternal size Ethnic origin Paternal influence less important Fetal Infections TORCH = Toxoplasmosis, Other, Rubella, Cytomegalovirus and Herpes Remember Syphilis and HIV Fetal Abnormalities Especially chromosomal abnormalities such as Trisomy 21, 13&16

Causes of Asymmetrical IUGR Anything that reduces Maternal-Uterine-Placental to Fetus transfer of oxygen and nutrients Maternal smoking and malnutrition Severe maternal anaemia Chronic maternal disease Maternal hypertension especially pre eclampsia Uterine malformations Some placental diseases Maternal thrombophilias congenital or acquired Recurrent antepartum haemorrhage An idiopathic group

A SFD uterus is more serious when… The mother was underweight to begin with She has not gained weight appropriately There is a past history of IUGR or pregnancy loss A condition known to be associated with IUGR is also diagnosed Pre eclampsia Recurrent APH Chronic maternal disease or anaemia

Management of the SFD baby Accurate diagnosis Is the baby salvageable? Mother at risk? Steps that improve M-U-P-Fetal transfer of oxygen and nutrients Stop maternal smoking Bed rest Correct anaemia Monitor fetal growth and well being There is little point in ultrasound at less than 2w intervals Timely delivery Must weigh up the risks of induced delivery against the risk of remaining in utero

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