Saling's method: assessment of the fetus in labor
Saling's method is a technique for obtaining fetal capillary blood directly during labor after the rupture of amniotic membranes.
- Technique: a metal amnioscope tube with fiber optics is inserted through the birth canal.
- Sampling: after visualizing the presenting part (head or buttocks), skin scarification is performed to a depth of up to 2 mm.
- Important rule: blood is collected into a heparinized capillary without contact with air and amniotic fluid.
Analysis of the obtained blood allows for the assessment of acid-base balance (ABB), including pH, $pCO_2$, $pO_2$, and lactate levels.
Invasive prenatal diagnosis
To detect genetic disorders and malformations, invasive interventions under ultrasound guidance are used:
- Chorionic villus sampling: performed at 8–12 weeks transcervically or transabdominally.
- Cordocentesis: puncture of umbilical cord vessels. In case of high fetal activity, neuroblockers (e.g., pipecuronium) may be used.
- Cytogenetic analysis: study of the karyotype using amniocytes, lymphocytes, or chorionic cells.
Modern methods, such as FISH analysis and molecular genetic studies (microarrays), allow for a detailed examination of the chromosome set and the identification of monogenic defects.
Screening and pathology markers
Prenatal diagnosis up to 22 weeks includes non-invasive methods:
| Timeframe | Method | Goal |
|---|---|---|
| 11–14 weeks | Ultrasound + biochemistry | Detection of congenital malformations (CM) and echomarkers |
| 18–21 weeks | Expert-level ultrasound | Detailed fetal anatomy |
The key echomarker in the 1st trimester is nuchal translucency (NT). In the 2nd trimester, cranial shape anomalies ("lemon", "banana"), ventriculomegaly, and hyperechogenic bowel acquire diagnostic significance.
A-B-C: Amnioscopy (visualization), Biopsy (material), CM (congenital malformations detection).
Class and exam questions
In which cases are neuroblockers used during cordocentesis?
They are used in cases of pronounced fetal motor activity, which prevents the accurate performance of umbilical cord vessel puncture.
Which acid-base balance parameters are most important in Saling's method?
Critically important are blood pH, partial pressure of oxygen ($pO_2$) and carbon dioxide ($pCO_2$), as well as lactate levels.
Why is contact with air prohibited during blood collection using Saling's method?
Contact with air distorts blood gas parameters, making an adequate assessment of the fetal condition impossible.
What else to study on this topic
- Comparative characteristics of transcervical and transabdominal approaches in chorionic villus sampling.
- Complications of invasive procedures: incidence of premature rupture of membranes (PROM) and perinatal loss.
- Principles of medical genetic counseling in the detection of chromosomal abnormality markers.
- Advantages of genome-wide microarray hybridization over classical karyotyping.
- Differential diagnosis of chromosomal pathology echomarkers in the 2nd trimester.
Master the entire topic in the "Obstetrics and Gynecology" course
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