Routine tests in first trimester

1. Blood and urine tests usually at 10-12 weeks – we require various blood samples and 1 urine sample to perform these tests:

a) Full blood count (FBC) – screens for anaemia and thalassaemia. Anaemia is diagnosed when haemoglobin level is less than 11.0 g / dl, and alpha- or beta- thalassaemia should be suspected when mean cell volume (MCV) is less than 80 fl. Haemoglobin electrophoresis is indicated if MCV is less than 80 fl, and would include the FBC and haemoglobin electrophoresis of the partner as well. DNA gene probes for thalassaemia may be indicated if alpha thalassaemia is suspected.

b) Ferritin and vitamin B12 levels - screens for iron deficiency and vitamin B deficiency. Iron deficiency is common amongst women who as blood is lost during their regular periods, especially if they are heavy, and / or whose diet is poor in terms of iron intake e.g. vegetarians and vegans. Vitamin B12 deficiency is common amongst women whose diet is poor in terms of vitamin B12 intake e.g. vegetarians and vegans. Oral supplements may be given to reduce the risk of such deficiencies. Untreated, this may lead to symptoms like fatigue and anaemia. Severe anaemia may increase the risk of growth restriction and preterm birth for the pregnancy, and severe maternal iron deficiency may also increase the risk of fetal iron deficiency which may not optimize the memory and concentration functions of the baby.

c) Infection screen for Hepatitis B, syphilis, HIV (human immunodeficiency virus) and CMV (cytomegalovirus). If positive, there are strategies to reduce the risk of transmission of the infection to the baby.

i) For mothers who are positive with Hepatitis B surface antigen, checking the

Hepatitis B viral load is needed at 28 weeks. Mothers who are high in Hepatitis B

viral load should have antiviral medications during pregnancy to reduce the risk of

transmission to the baby. On top of that, the neonatologist will arrange for Hepatitis

B antibodies and vaccination to the baby to prevent transmission to the baby.

ii) For syphilis, the use of high dose penicillin before 16 weeks of pregnancy is very

effective to almost eliminate the risk of congenital syphilis to the baby.

iii) For HIV, the use of antiviral medications to suppress the HIV viral load, avoidance

of breast feeding and choosing elective Caesarean section would drastically

reduce the risk of transmission of the HIV to the baby.

iv) For CMV, the use of high dose valaciclovir early on in pregnancy to those who

have been infected with CMV in the first trimester has been shown to reduce the

risk of transmission of CMV to the fetus (see

https://pubmed.ncbi.nlm.nih.gov/37473793/). We do a step-wise screening for CMV

infection in the first trimester. We start off with CMV IgM at about 12 weeks. If

positive, we check for CMV IgG. If CMV IgG is positive, we check for CMV IgG

avidity. If CMV IgG avidity is low, it indicates an infection in the last 3 months.

Amniocentesis from 17 weeks onwards can be performed to check if CMV particles

can be found in the amniotic fluid. If CMV cannot be found in the amniotic fluid, it is

very unlikely that the baby would suffer any major consequences from being

exposed to the CMV infection during the first trimester.

d) Immunity screen for Rubella - If negative, consider rubella vaccination before the next pregnancy. It prevents the potential of contracting rubella during the first or second trimester of pregnancy that may affect the fetus severely.

e) Pre-existing diabetes mellitus – glucose and HbA1c levels. Those with pre-existing diabetes mellitus and with high HbA1c during pregnancy are faced with higher risks of abnormalities to the fetus.

f) Blood group and Rhesus type - This screens for Rhesus negative state in the mother. If the mother is Rhesus negative, injection with Rhogam injections during certain scenarios would reduce the risk of a blood problem to future, or even current, babies.

g) Screening for antibodies to atypical red blood cell antigens - This screens for potentially harmful antibodies in the mother that could cross the placenta and bind to the red blood cells of the fetus and possibly causing heart failure in the foetus, and also possible antibodies that may cause a reaction if an incompatible blood type is used for blood transfusion.

h) Placental growth factor (PlGF) - This allows for more accurate calculation of the risk of pre-eclampsia and intrauterine growth restriction before 37 weeks. Low dose aspirin (150 mg once a night) and high dose calcium supplements (at least 1.5-2 g per day) started before 16 weeks reduces the risk of pre-eclampsia and fetal growth restriction before 37 weeks for those who are judged to be high risk.

i) Screen for asymptomatic urinary tract infection with urine microscopy. If it shows possibility of urinary tract infection, a urine culture would be indicated and antibiotics may be necessary as it may reduce the risk of late miscarriages and preterm labour.

j) Non-invasive prenatal test (NIPT) - Many NIPTs are now available where blood is taken and DNA belonging to the fetus (or more accurately, the placenta) is analysed to offer very effective screening for common chromosomal abnormalities (like Down syndrome, Edward syndrome, Patau syndrome, Turner syndrome) and some atypical chromosomal abnormalities. For the atypical chromosomal abnormalities, different companies now claim to be able to screen different combinations of such conditions. We can do this test as early as 9+ weeks, with results available usually in 2 weeks. See https://www.drtonytan.com/post/non-invasive-prenatal-test-nipt for more information.

k) Other tests - these may include:

i) toxoplasmosis screening if you have frequent contacts with cats or have been

exposed to uncooked or partially cooked meats like beef

ii) carrier screening - this screens for 400+ autosomal recessive and X-linked

recessive conditions in the couple. There is up to 2% chance of the couple having

an increased risk of having a child with a genetic condition. This screening is not

routinely offered in Singapore but is already routinely offered in the US and

Australia. More information can be found in these links:

https://www.baylorgenetics.com/news/what-is-carrier-screening-geneaware/

https://www.nejm.org/doi/full/10.1056/NEJMoa2314768

Do let us know if you want to discuss this further.

iii) micronutrient screening - this may be necessary for those who have undergone

bariatric surgery as it may impair the absorption of certain micronutrients in the

body.

2. First Trimester Scan (FTS) between 12-13 weeks

The FTS is designed to screen for 4 groups of problems in pregnancy:

a) Risks of common chromosomal abnormalities (including Down syndrome [Trisomy 21], Edward syndrome [Trisomy 18] and Patau syndrome [Trisomy 13]) using Fetal Medicine Foundation (FMF) software. This allows the detection of 90% of Down syndrome, 90% of Edward syndrome and 90% of Patau syndrome.

b) Early structural abnormalities such as anencephaly (absence of skull), exomphalos (protrusion of intestines through an abdominal wall defect), megacystis (enlarged bladder), etc.

c) Risk of early pre-eclampsia requiring delivery 37 weeks (i.e. a serious condition during pregnancy characterised by high blood pressure with proteins in the urine). If left untreated, pre-eclampsia tends to progress and may become very serious. As the treatment of pre-eclampsia is delivery, we are most worried if the pre-eclampsia occurs early (i.e. before 37 weeks) which may require us to delivery early. If the risk of pre-eclampsia is raised, calcium supplementation of at least 1 g / day and low dose aspirin of 150 mg taken in the night reduce the risk of this complication.

d) Risk of fetal growth restriction before 37 weeks which may require early delivery. If fetal growth restriction is detection, the fetus needs to be closely monitored with fetal movement chart, regular measurements of the fetus and regular Doppler studies of the blood flow within the baby, and also cardiotocography (CTG) later in the third trimester. When the fetal status is non-reassuring, early delivery may be indicated. Low dose aspirin of 150 mg taken in the night and calcium supplementation of at least 1 g / day may reduce the risk of fetal growth restriction. However, there is less data on low dose aspirin for prevention of this condition.