# Invasive Prenatal Diagnostics: A Cornerstone of Perinatal Management
## 2 Techniques of Invasive Diagnostics
### Amniocentesis
#### 2.1.4 Biochemical Analysis  
_Footal lung maturation_--In 1971, [PERSON] et al. [162] first introduced the concept of assessing the degree of foetal lung maturation (FLM) with the lecithin/sphingomyelin ratio in amniotic fluid. The idea was to estimate the risk of neonatal respiratory distress syndrome (RDS) in the case of an iatrogenic preterm delivery. Their study showed that the concentration of phospholipids in amniotic fluid, represented by lecithin, reflected alveolar stability. After 35 weeks of gestation, they observed a sharp peak in lecithin concentration, which, if referred to sphingomyelin, was a credible source of information regarding the chance of developing RDS. This finding was consistent with a low incidence of this complication after 34 weeks of gestation. However, further research concerning this topic showed very poor positive and negative predictive value for this examination [163, 164]. Therefore, in 2019, the American College of Obstetricians and Gynaecologists (ACOG) provided guidelines to clinicians regarding the utility of FLM testing [165]. Since then, FLM testing is not recommended to guide the timing of delivery. _Rh Disease_--One of the first reported applications of amniocentesis was the management of Rh disease. In 1952, [PERSON] et al. [166], and later, others [167, 168], introduced a method to assess the severity of foetal haemolysis associated with maternal immunisation. In the case of detecting maternal antibodies in the Indirect Antiglobulin Test, amniocentesis was carried out in biweekly or weekly intervals. Subsequently, the samples were centrifuged and analysed with spectrophotometric tracing. An increased concentration of the bile pigment was found to be associated with the risk of foetal death. Therefore, labour induction was conducted at 36-38 weeks of gestation [167]. In 1963, [PERSON] [168] reported the first successful intrauterine transfusion. After injecting a contrast material, an X-ray scan, an _Aminogram_, was taken. Using the gastrointestinal tract as a guide, [PERSON] passed a needle through the maternal abdominal wall and the uterine wall into the foetal peritoneal cavity [169]. Subsequently, in group 0, Rh-negative blood from a donor was transfused. This is considered to be the earliest step of foetal interventions. However, because of its high sensitivity and non-invasiveness, ultrasound Doppler evaluation of median cerebral artery flow velocity is an accepted method of assessing foetal anaemia. Upon suspicion of anaemia, the diagnosis should be confirmed through the procedure of cordocentesis. _Alpha-fetoprotein (AFP)_--First described in 1956 by [PERSON] [170], AFP is a foetal serum protein produced by the yolk sac, liver, and gastrointestinal tract mucosa [171]. It is excreted with urine and therefore can be detected in amniotic fluid from the 12 th week of gestation to birth in variable concentrations [172]. It has found a wide application in predicting various foetal abnormalities. In the 1970s, it was proved that abnormally high levels of AFP were present in the amniotic fluid of foetuses with neural tube defects [173]. Since ultrasound was not yet commonly used, it received enthusiastic acceptance. In 1989, a study by [PERSON] et al. [174] showed a significantly lower level of AFP in the maternal serum of patients with trisomy 21 pregnancy. This finding allowed for the introduction of a novel second-trimester screening method for Down syndrome called the quadruple test in 2003 [175]. While the usefulness of amniotic fluid-AFP in diagnosing foetal abnormalities is well established, a recent study by [PERSON] et al. [171] indicated that it can be a valuable screening tool for adverse perinatal outcomes. In a group of more than 7000 patients, they showed that a concentration of AFAFP of >2 MoM had a high prediction rate of pretermdelivery, stillbirth, foetal growth restriction, and hypertensive disorders.