Fræðigrein

Objective: To evaluate the effects of normal vaginal delivery (NVD) on oxygen transport to the fetus.

Study group and methods: Fifty newborn infants born by NVD and as a control group 50 infants born by elective Cesarean section (ECS) were studied. Factors reflecting oxygen transport to the fetus were measured in venous and arterial cord blood: pH, partial pressure of oxygen (pO2) and carbon dioxide (pCO2), oxygen saturation (SO2), blood oxygen content, base deficit, and lactic acid concentrations, erythropoietin concentrations, number of nucleated red blood cells and haemoglobin concentrations.

Results: There was no significant difference in venous blood oxygen content between the two groups of infants. However, arterial blood oxygen content was significanlty lower in the infants born by ECS than in those born by NVD (p<0.001). Infants born by NVD had significantly lower pH (p<0.001), greater base deficit (p<0.001), higher lactic acid (p<0.001) and erythropoietin concentrations (p=0.01), more nucleated red blood cells (p=0.004), and higher hemoglobin concentrations (p=0.002) in venous blood than in the infants born by ECS. pH was lower (p<0.001) and lactic aicid concentrations were higher (p<0.001) in arterial blood than venous blood in both groups of infants.

Conclusions: (1) NVD causes reduction in oxygen transport to the fetus, resulting in acidosis and stimulation of blood forming tissues. (2) ECS is associated with more reduction in umbilical arterial cord blood oxygen content than NVD. (3) When evaluating acidosis in newborns after delivery it is more reliable to measure pH and lactic acid concentrations in arterial rather than venous cord blood.

Tabel 1. Demographic data.

	Normal vaginal delivery	Elective cesarean section	p-value
Maternl age (years)	28,9 + 5,0	31 + 4,8	0,03
Gestational age (weeks)	39 w. 6 d. + 9 d.	39 w. 1 d. + 5 d.	0,008
Sex (M/F)	24/26	23/27	0,8
Birthweigth (g)	3782 + 476	3703 + 484	0,4
Length (cm)	52,0 + 1,7	50,9+ 1,7	0,002
Head circumference (cm)	35,8 + 1,2	36,2 + 1,2	0,12
Apgar 1 minute	8 (5-10)	8 (7-10)	0,1
Apgar 5 minute	9 (7-10)	9 (8-10)	0,7

Table 2.  Comparison of acid-base balance and factors which determine oxygen delivery to the fetus in cord venous vs. cord arterial blood.

	Venous cord blood	Arterial cord blood	p-value
Normal vaginal delivery
pH	7,30 + 0,09	7,18 + 0,09	<0,001
pCO2  (mmHg)	42,7 + 10,7	57,9 + 11,5	<0,001
pO2  (mmHg)	30,3 + 7,2	21,7 + 7,9	<0,001
SO2  (%)	60,9 + 16,2	36,2 + 15,8	<0,001
Oxygen content*	13,5 + 3,4	7,8 + 3,2	<0,001
Base excess (mmol/L)	- 5,9 + 3,7	- 8,4 + 4,6	<0,001
Lactate (mmol/L)	4,5 + 1,7	5,3 + 1,6	<0,001
Elective cesarean section
pH	7,36 + 0,04	7,29 + 0,05	<0,001
pCO2   (mmHg)	42,5  + 5,0	54,6 + 5,9	<0,001
pO2  (mmHg)	27,6 + 5,5	14,2 + 3,9	<0,001
SO2  (%)	62,7 + 13,8	22,6 + 10,6	<0,001
Oxygen content*	13,1  + 3,1	4,7  + 2,4	<0,001
Base excess (mmol/L)	- 1,4 + 1,7	- 1,6 + 2,3	0,6
Lactate (mmol/L)	1,9 + 0,7	2,4 + 0,9	<0,001

* Oxygen content: ml O2 / ml blood

 

Figure.Acid-base balance and factors which determine oxygen delivery to the fetus, measured in cord blood of newborns born by normal vaginal delivery and by elective cesarean section.                                                                                                   

* Oxygen content: ml O2 / ml blood

** Nucleated red blood cells: (x 1000 / L)

*** SO2 difference: The difference in SO2 in arterial vs.venous blood.