European Journal of Obstetrics & Gynecology and Reproductive Biology, pages 97 - 102
To investigate if repeat (≥3) fetal scalp blood sampling (FBS) is associated with increased risk of caesarean delivery and worse neonatal outcome than occasional (1–2) FBS.
Prospective cohort study of women undergoing intrapartum FBS at Karolinska University Hospital, Sweden. FBS with lactate analysis was performed if the attending doctor found the cardiotocography (CTG) tracing suspicious or abnormal. Lactate concentration was measured bedside. As a routine in all deliveries, acid-base analyses were performed on umbilical artery and vein blood immediately after delivery. Main outcome measures were metabolic acidemia in umbilical artery at delivery, Apgar score <7 at 5 min and caesarean delivery.
During the study period there were 2134 FBSs performed on 1070 laboring women with a median of two samplings (range 1–8). There were no differences in Apgar score <7 at 5 min or metabolic acidemia in umbilical artery blood at birth between labors with 1–2 FBS and ≥3 FBS. Among women who underwent 1–2 FBS, 23% had a caesarean delivery as compared with 42% of those having ≥3 FBS. After adjustment for confounders, repeat FBS remained an independent risk factor for caesarean delivery (adj OR 2.05; 95%C.I 1.5–2.8).
Fetal monitoring with repetitive FBS (≥3) during labors with CTG changes is safe for the baby, but the rate of caesarean delivery is doubled as compared to labors where 1–2 FBS are needed. Still, more than 50% of women with repetitive FBS will be delivered vaginally, and 1/3 of these spontaneously.
Keywords: Fetal monitoring, Cardiotocography, Metabolic acidosis, Fetal distress, Fetal blood sampling.
Fetal scalp blood sampling (FBS) was developed as a method of intrapartum fetal surveillance parallel to the development of cardiotocography (CTG), and introduced in clinical practice in the 1960's, using pH analysis on fetal scalp blood. During the 1980's lactate analysis was evaluated for use in FBS, and is currently used at most labor wards in Sweden  . Intrapartum CTG has low specificity with many non-acidemic fetuses having CTG changes, and FBS with lactate analysis can be used to exclude metabolic acidemia in cases of non-reassuring CTG, as false negative tests are unlikely  . Since fetal lactate increases specifically during anaerobic metabolism, FBS also reliably detect fetuses at risk of developing hypoxemia, , and .
Lactate concentration in fetal scalp blood correlates with lactate and pH in the umbilical artery, and is shown to be more sensitive than fetal scalp pH in predicting low Apgar score at 5 min and hypoxic ischemic encephalopathy  . The cut-off value is based on a large population, and has a good agreement with gold standard pH analysis regarding frequency of intervention and . Cut-off values for intervention must however always be considered in the light of the meter that is used.
The guidelines for use of FBS lies in the hands of CTG interpretation, which is affected by inter observer variation, , , and . If the CTG tracing has indicated FBS early in first stage of labor or if labor is prolonged, there are no clear guidelines how to continue fetal surveillance during the remaining part of labor if the first FBS shows normal results. The National Institute of Health and Clinical Excellence (NICE) has published the recommendation that a resident should obtain an obstetric opinion from a consultant if a third FBS is considered necessary, but this recommendation is based on consensus rather than scientific evidence  . A retrospective study from 2011 showed an increased risk of operative delivery and admission to neonatal intensive care unit (NICU) in cases with FBS in early labor (cervical dilatation ≤3 cm), but no increased prevalence of birth acidemia. However, the chance of a vaginal delivery was still 48%  .
We hypothesized that in most cases with a normal result at the first FBS, there is no development of acidemia. Prolonged duration of mild/moderate CTG changes, causing repetitive FBSs during labor, might influence the threshold for operative interventions, but without increased frequency of fetal or neonatal acidemia or worse neonatal outcome. The aims of the present study were to evaluate if women with repetitive FBS (≥3) during labor had increased rates of fetal acidemia, operative interventions and/or worse neonatal outcome, as compared with women having had one or two FBS during labor.
Materials and methods
We performed a prospective observational cohort study of women undergoing FBS during labor. The study was carried out at the labor ward at Karolinska University Hospital from February 2009 through February 2011. Inclusion criteria were simplex pregnancy, gestational length ≥34 weeks, cephalic presentation and indication for FBS during labor according to the attending obstetrician. Ethical approval was granted by the Regional Ethics Committee of Stockholm (2008/1618-31, 2011/478-32).
Intrapartum fetal surveillance with CTG followed Swedish guidelines  . All women had an admission CTG and if they were considered at low risk, they had intermittent CTG monitoring during labor every 2 h and in between auscultation of the fetal heart every 15 min  . If they were considered at high risk, had epidural or were commenced on oxytocin for augmentation of labor, they had continuous CTG monitoring. CTG interpretation followed the guidelines of the Swedish Society of Obstetrics and Gynecology (SFOG)  , which are based on the guidelines of the International Federation of Gynecology and Obstetrics (FIGO)  . If a CTG trace was non-reassuring, but not indicative for immediate delivery, the attending doctor could decide upon FBS, which then was performed according to clinical routine, with the use of amnioscope, wiping the scalp of the fetus dry from amniotic fluid and applying silicone gel. After incision, approximately 5 μL was collected into a capillary tube, and analysis of lactate concentration was immediately performed at the bedside using Lactate Pro™ (KDK Corp. Kyoto, Japan). The meters were calibrated every 50th analysis, and the reported coefficient of variation is ≤4%  . Action was taken according to previously published guidelines  .
As a second FBS often is an immediate recheck to exclude contamination of amniotic fluid or analysis error, we chose to divide the cohort into those with 1–2 or three or more FBS.
Sampling of umbilical artery and vein blood was performed immediately after delivery in all labors as a clinical routine. Complete acid-base status was analysed using ABL 800 Flex, (Radiometer, Copenhagen) and metabolic acidemia was defined as pH < 7.05 and base deficit (BD)blood > 12 mmol/L  . Gestational age was based on ultrasound scanning performed in the first or early second trimester. Small and large for gestational age (SGA and LGA, respectively) was defined as a birth weight more than two standard deviations below (SGA) or above (LGA) the mean birth weight for gestational age according to the sex-specific Swedish fetal growth curves  .
Statistical analysis was carried out using Statistica for Windows, version 12.0, (Statsoft Inc., Tulsa, OK, USA). Data are reported as medians, range and percentage due to non-normal distribution. Chi-square test and Fisher's exact test were applied for comparison of proportions, and Mann–WhitneyU-test was used for comparison of continuous variables between groups. Logistic regression was used to calculate odds ratios (OR), 95% confidence intervals (CI) and to adjust for possible confounding effects of maternal age, gestational age, parity, previous caesarean delivery, induction of labor and oxytocin augmentation. Due to non-linearity of the continuous variables, maternal and gestational age were categorized as well as time from first sampling to delivery and cervical status at first FBS. All effects are presented. The model was validated with Hosmer Lemeshow test.p < 0.05 was considered to be significant.
During the study period there were 2134 FBS performed on 1070 laboring women, which constituted 11% of all deliveries at this labor ward. FBS was used from a cervical dilatation of two cm and two thirds of the women had the first FBS taken during 1st stage of labor. Characteristics of the study population are shown in Table 1 . In this population with FBS during labor, the proportion of nulliparous women was markedly higher than in the total delivering population (72%), labor was more often induced (35.5%), and 10% of the women had a history of previous caesarean delivery (27.4% of the multiparous). There were 297 women (27.8%) having at least one maternal complication (e.g. hypertension, preeclampsia or diabetes), 165 (15.4%) had at least one fetal complication (e.g. known intrauterine growth restriction, oligo- or polyhydramniosis) and 66 (5.5%) had both maternal and fetal complications.
|Total population N = 1070||1–2 FBS N = 795||≥3 FBS N = 275||p-Value a|
|Maternal age (years)||≤24
|Nulliparous||772 (72.1)||563 (70.8)||209 (76.0)||0.10|
|Previous caesarean delivery||109 (10.2)||75 (9.4)||34 (12.4)||0.16|
|Gestational age (weeksdays)||340–366
|Induction of labor||380 (35.5)||263 (33.1)||117 (42.5)||0.005|
|Birth weight group b||SGA
|Birth weight (grams)||<2500
a p Calculated with Chi square test between subgroups.
b SGA < 2 SD and LGA > 2 SD from the mean according to the sex-specific Swedish fetal weight curves  .
SGA, AGA, LGA = small, appropriate and large for gestational age.
The median number of FBS was two, 48% of the women had only one FBS and the range of FBS was 1–8. 795 Women had one or two samplings taken during their course of labor, and 275 women underwent three or more FBS.
Median time from first FBS to delivery was 88 min for those with 1–2 samplings and 240 min for those with 3 or more samplings (p < 0.001). The median cervical dilatation at the first FBS was 10 cm in the group with 1–2 samplings and 6 cm in the group with ≥3 samplings (p < 0.001). There were no differences in proportions of nulliparous women or women with a history of caesarean delivery between the groups. Median maternal age was 31 years and did not differ between groups, but there was a higher proportion of women with induced labor in the group with three or more FBS, and their gestational age at delivery was on average three days longer (median 40 weeks + 5 days vs. 40 weeks + 2 days).
At the last FBS, the median lactate concentration was higher in the group with multiple samplings ( Table 2 ). The lactate concentration at the last FBS was positively correlated to the total numbers of FBS performed during labor ( Fig. 1 ). The proportion of cases with acidemic levels of lactate concentration (>4.8 mmol/L) at the last FBS was also higher in this group, and the difference was unchanged when cases with active pushing prior to sampling was excluded. Indication for instrumental or operative delivery was more often fetal distress in the group with ≥3 samplings, compared with the group with one or two samplings ( Table 2 ).
|Cases with 1–2 FBS during labor||Cases with ≥3 FBS during labor||p-Value|
|Lactate concentration (mmol/L) median (range)||2.7
|Cases with lactate >4.8 mmol/L N (%)||99/795 (12.4)||76/275 (27.6)||<0.001 b|
|Cases with fetal distress as indication for delivery c N (%)||228/426 (53.5)||162/221 (73.3)||<0.001 b|
a p-Value calculated with Mann–Whitney U test.
b p-Value calculated with Chi-square test.
c Instrumental vaginal and caesarean delivery.
Among women who underwent one or two FBS, 46% had a spontaneous vaginal delivery (SVD) in contrast to 19% of those having three or more FBS during labor ( Fig. 2 ). Of those delivered operatively (ventouse or caesarean), 38% had three or more FBS, compared with 12% of those delivered normally ( Table 3 ). The proportion of caesarean delivery in labors with increasing total numbers of FBS is shown in Fig. 3 .
|1–2 FBS||≥3 FBS||p-Value a|
|Apgar < 7 at 5 min b||9/794 (1.1)||6/272 (2.2)||0.19|
|Umbilical artery pH < 7.0 c||7/618 (1.1)||2/234 (0.9)||0.72|
|Umbilical artery pH < 7.10 c||34/618 (5.5)||7/234 (3.0)||0.12|
|Metabolic acidemia in umbilical artery c||11/616 (1.8)||3/234 (1.3)||0.61|
|Resuscitation||3/795 (0.4)||2/275 (0.7)||0.46|
|Respirator care/CPAP||22/795 (2.8)||10/275 (3.6)||0.47|
|Meconium aspiration||5/795 (0.6)||0/275 (0.0)||0.19|
|Hypoxic ischemic encephalopathy||0/795 (0.0)||1/275 (0.4)||0.09|
|NICU admission||42/795 (4.3)||17/275 (6.2)||0.57|
|Spontaneous vaginal delivery||366 (46.0)||52 (18.9)||<0.001|
|Instrumental vaginal delivery||244 (30.7)||108 (39.3)||0.009|
|Caesarean delivery||185 (23.3)||115 (41.8)||<0.001|
a p Calculated with Chi-square test.
b Four cases with no Apgar score noted.
c 218 Cases with no or incomplete umbilical blood samples noted, metabolic acidemia defined as pH < 7.05 and base deficitblood > 12.
There were no differences between the groups concerning short-term neonatal outcome. The proportions of neonates with low Apgar score at 5 min, or metabolic acidemia in umbilical artery did not differ, nor did proportions of babies needing respiratory support or admission to the NICU. There were five cases with meconium aspiration in the group with maximum two FBS during labor, and none in the group with three or more samplings. There was one case of hypoxic ischemic encephalopathy (HIE) and no case of perinatal death in the study population ( Table 3 ).
Women with a previous caesarean delivery, those with induced labor and nulliparous women had an increased risk of caesarean delivery. Compared to women with 1–2 FBS, women with three or more FBS still had a two-fold increased risk of caesarean delivery in the adjusted analysis ( Table 4 ). FBS in early labor (cervical status 2–4 cm) was associated with an increased risk for caesarean delivery with an adjusted OR of 4.5. Adjustment for time from first FBS and cervical status at first FBS did not substantially reduce the OR of multiple FBS ( Table 5 ).
|N||Caesarean delivery rate (%)||Crude OR||95% CI||Adj OR a||95% CI|
|Parity and previous caesarean||Multiparous without previous caesarean||189||20.1||Ref||Ref|
|Multiparous with previous caesarean||109||34.9||2.13||1.25–3.62||1.97||1.14–3.41|
|Gestational age||<37 w||36||27.8||1.13||0.53–2.39||1.12||0.52–2.41|
|Start of labor||Spontaneous||690||23.8||Ref|
|FBS during labor||≤2 FBS||795||23.3||Ref||Ref|
a Adjusted for all other parameters in the model.
|N||Caesarean delivery rate (%)||Crude OR||95% CI||Adj OR||95% CI|
|Cervical dilation at FBS||2–4 cm||117||59.8||4.68||3.14–6.97||4.53||2.99–6.86|
|Duration from 1st FBS to birth||<3 h||672||24.4||Ref||Ref|
|FBS during labor||1–2||795||23.3||Ref||Ref|
Neonatal outcome in terms of umbilical artery acid-base status, Apgar score or need of NICU care was not impaired when CTG changes had caused multiple samplings during labor, compared with occasional sampling. The chance of a vaginal delivery decreased when FBS during labor exceeded two samplings, and women who underwent ≥3 FBS during the course of labor had a doubled risk of caesarean delivery compared with those having only 1–2 FBS. However, still about 60% of parturients with ≥3 FBS had a vaginal delivery and 19% had a spontaneous vaginal delivery. FBS in early labor was associated with an increased risk of caesarean delivery, and if cervical dilatation at first FBS was ≤4 cm, the proportion of vaginally delivered was only 40%.
The use of FBS varies largely between countries, with reported frequencies between 3 and 15% in some countries, , and , and essentially none in other. The attitude toward the use of FBS can be considered liberal at the labor ward where this study was conducted, with a frequency of 11% of all labors, but is comparable to other countries where FBS is a part of intrapartum fetal surveillance routines  .
Repetitive FBS during labor can partly be explained by appearance of CTG changes early in labor. Fetal surveillance with FBS started earlier in the first stage of labor in the group with three or more FBS. It is reasonable to interpret multiple FBS in labor as prolonged duration of a CTG tracing that is worrisome for the attending physician but not indicative of immediate delivery. To our knowledge, there are no earlier prospective clinical studies concerning outcome after fetal surveillance with repetitive FBS throughout labor.
In spite of a larger proportion of lactacidemia in fetal scalp blood at the last FBS in the group with multiple FBS, there were no more cases of depressed new-borns or acidemia in umbilical artery. This supports earlier findings that the increase in lactate concentration in fetal scalp blood is an early marker of fetal hypoxia and , and that the cut-off for recommendation of delivery is adequately set, aiming for delivery of a healthy non-acidemic baby. The cut-off value is set well below levels predictive of metabolic acidemia in umbilical artery  , which enables prevention of birth acidemia. This is a primary goal with intrapartum fetal surveillance—to prevent and not to predict.
We found a doubled risk of caesarean delivery if CTG-changes had caused more than two FBS during labor, and this increased risk was only marginally affected by known risk factors for caesarean delivery, including previous caesarean delivery, induction of labor, and nulliparity. These results are in accordance with a recent retrospective study by Heazell et al, who found that FBS in early labor as well as multiple FBS increased the risk of caesarean delivery  . In contrast to the study results of Heazell et al., we did not find an increased frequency of NICU admission in cases with multiple FBS during labor.
It is not possible to draw conclusions about the impact the use of FBS might have per se on the caesarean delivery rate, since the entire study population consisted of women with FBS performed. Critics of the intrapartum use of FBS argue that there is no shown benefit of FBS as an adjunct to CTG and , and refer to the meta-analysis of EFM where subgroup analysis by access to FBS was done  . The comparison was however between RCT:s with access to FBS in all arms, and RCT:s without the adjunct of FBS, and the different RCT:s varied largely in inclusion criteria and study populations. The only study that randomized to CTG with or without FBS was the Denver study, with approximately 230 women in each arm, and a reported caesarean rate of 18% in the CTG group and 11% in the CTG + FBS group, although without reaching statistical significance  . In a recent review Jørgensen and Weber concluded that the use of FBS as a supplement to CTG can reduce the risk of operative delivery, and can provide additional information on fetal wellbeing and reserves before decisions on need for and timing of operative delivery  .
The strength of this study is the prospective study design, including all consecutive cases with FBS during labor at a large obstetric service center with approximately 4500 annual deliveries during the two years study period. The risk of failed attempts to perform FBS is small since lactate analysis was used. The reported frequency of sampling or analysis failure is 1.2–1.7% compared with up to 20% for FBS with pH analysis and . There was also a high proportion of cases with acid base balance in umbilical cord blood (80%). The risk of unreported cases with FBS is small since the FBS results were routinely noted in the medical record.
All women in this study underwent FBS and thus had a non-reassuring CTG tracing; it is therefore not suitable to generalize the findings to the general delivering population. We believe the results of the study can be used in labors where FBS are undertaken, when planning the remaining part of labor.
Another possible limitation is that the number of FBS undertaken could be inversely related to the physician's experience of CTG interpretation, i.e. junior doctors may take more samples. There is always at least one consultant of the two doctors on call at the labor ward where the study was performed. We therefore find it unlikely that the experience of the doctor handling the labor would differ between the groups.
We found an increased rate of lactacidemia in fetal scalp blood without negative effect on neonatal outcome in labors where the attending doctor found indication for ≥3 FBS during labor. It is reassuring that there were no more cases with low Apgar score, metabolic acidemia in umbilical artery or admissions to NICU in the group with repeat FBS. The risk of caesarean delivery was doubled compared with labors where occasional sampling was done.
Signhild Engkvists Stiftelse, Stockholm County Council
Labors with ≥3 fetal scalp blood samplings has no worse neonatal outcome, but a doubled caesarean rate as compared to labors with 1–2 FBS.
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a Department of Women's and Children's Health, Karolinska Institutet, Karolinska University Hospital, 17176 Stockholm, Sweden
b Clinical Epidemiology Unit, Department of Medicine, Karolinska Institutet, Karolinska University Hospital, 17176 Stockholm, Sweden
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