Maternal venepuncture, including glucose tolerance testing
Venepuncture is the entering of a needle into a vein in order to obtain a specimen of blood. Venepuncture can also be used for the administration of a drug intravenously in an emergency situation. The physiological changes during pregnancy, for example increased blood supply and generalised warmth of the woman, promote vasodilatation and thus the veins are more visible. Therefore venepuncture performed on a pregnant woman is considered to be easier than at other times.
- Antenatal ‘booking’ bloods
- Assessment of full blood count and rhesus antibodies
- Fetal antenatal screening tests
- Ongoing monitoring of existing medical conditions, e.g. haemoglobinopathies, epilepsy, diabetes, pre-eclampsia
- Cross matching or ‘group and save’.
This list is not exhaustive.
It is the midwife’s role to provide comfort, privacy, dignity and respect at all times. This will help to ensure that the woman is able to give informed consent. Some women present with a phobia of needles that causes them great anxiety. The midwife should take time and provide support to improve the whole experience; this includes the use of coping strategies and ‘pain relieving cream’. The woman’s medical history should be considered as the cream can interact with some medications. Also, there is a time factor to consider as 1–5 hours are needed for the cream to work effectively.
The site normally used is in the antecubital fossa. Preference as to which arm needs to be discussed with the woman. The veins here are easily accessible and are the accessory cephalic, median cubital and basilic veins (Figure 47.1). Once a tourniquet is in place, assessment of the suitability of the vein can be made, considering size and mobility. Palpation will allow this assessment, ensuring that the vein is ‘full and bouncy’ with the consideration of valves (feels like a small nodule), arteries (pulse felt) and nerves. Although hitting a nerve is very rare, a knowledge of the position of the median and ulna nerves, plus ensuring the angle of needle insertion is within 10–30 degrees, will reduce the risk of occurrence.
Assessment of the condition of the skin should be made. There should be no bruising, scarring, infection or inflammation present. If present, another site must be found.
- Wash your hands with soap and water and put on non-sterile gloves and apron to reduce the risk of healthcare-acquired infection.
- Clean a plastic receiver using locally approved wipes. Leave to dry. Take off gloves and then wash and dry hands thoroughly.
- Gather equipment (Box 47.1), ensuring it is in date and the packaging is intact.
- It is important to discuss the procedure with the woman and gain informed consent.
- Ensure that this is the correct woman for venepuncture by checking details and required samples on the blood form verbally with the woman and/or if relevant by patient ID band.
- Ensure the woman is in a comfortable and accessible position, with a good light source.
- Position the tourniquet approximately 5–7 cm above the antecubital fossa.
- Assess and palpate the vein for quality and accessibility for venepuncture. The woman may be asked to make a fist a couple of times to make the vein ‘full and bouncy’ and therefore more easily visible.
- Remember the site of entry and release tourniquet.
- Decontaminate your hands and put on non-sterile gloves.
- As micro-organisms can enter the body or circulatory system at the skin site, cleanse the skin with approved decontaminant for 30 seconds and allow to dry for 30 seconds.
- Assemble required equipment and reapply tourniquet.
- Do not repalpate the vein as this will contaminate the skin.
- With the aim of anchoring the vein, use your non-dominant hand to apply slight tension to the skin just below the entry site.
- With your dominant hand, insert the needle with the bevel edge uppermost at a 10–30 degree angle (Figure 47.2).
- Attach the specimen bottles with your non-dominant hand considering the ‘order of the draw’ (Box 47.2) to reduce the risk of cross-contamination of additives.
- Bottles are self-filling but if blood does not appear then gently ‘adjust’ the position of the needle. Consider the potential for causing bruising.
- When the required samples have been obtained, release the tourniquet and remove the needle and syringe. Dispose of these directly into the sharps box.
- Immediately apply pressure (or ask the woman to do this) with gauze or cotton wool ball to the puncture site. With her arm horizontal, retain the pressure for at least 1 minute.
- If no allergies identified, apply a plaster dressing when bleeding has subsided.
- Take off gloves and wash and dry your hands.
- Label the blood bottles and complete the request form (Box 47.3) while the woman is still present.
- Dispose of equipment correctly and reclean the receiver.
- Document and act on results as they become available.
Glycosuria of >2+ (= 30 mmol/L) on one occasion and >1+ (= 15 mmol/L) on two occasions warrants further investigation for possible onset of gestational diabetes. Women who have presented with risk factors and/or previous gestational diabetes require a 2-hour 75 mg oral glucose tolerance test (OGTT). Those with previous gestational diabetes are tested twice: once at booking and then 24–28 weeks’ gestation. Those with risk factors are tested at 24–28 weeks’ gestation (NICE 2015).
Preparation for an OGTT is:
- The woman must not eat for 8–12 hours before the OGTT; she is permitted to drink water only.
- Local policy and procedure must be followed.
- Consider omission of certain medications as these can affect the overall test result – discuss this with the multidisciplinary team.
At the time of the test, a fasting blood sugar is taken. Then 75 mg of glucose is drunk by the woman. Blood is taken at hourly intervals up to 2 hours or just one sample is taken at 2 hours (RCOG 2013).
A diagnosis of gestational diabetes is made if a woman presents with:
- A fasting plasma glucose level of 5.6 mmol/L or above; or
- A 2-hour plasma glucose level of 7.8 mmol/L or above.
If the test results indicate a diagnosis of gestational diabetes, the woman should be offered a joint diabetic and antenatal review within 1 week (NICE 2015).