In the last two decades, many efforts were undertaken to improve estimates of fetal birth size trough sonographic assessment. Customizing fetal chart biometry [1, 2], different formulas for calculating fetal birth weight [3], repeated measurements [4] or probabilistic models [5] have been suggested. Additionally, clinical evaluation of the symphysis-fundal height (SFH) has been tested for predicting both lower and higher birth sizes [6, 7]. While predicting fetal birth size is useful for timing of birth in both low and high birth babies, we have previously shown [8, 9, 10] that SFH can predict adverse delivery outcomes in both induced and non-induced labors, independently from fetal weight. These studies, however, only assessed the delivery outcomes in full-term pregnancies. The aim of the present short report is to assess outcomes of birth in induced patients, encompassing also patients not at term, according to SFH values.

A prospective enrollment of a sample of induced patients was performed from January to December 2019 at the Obstetrics and Gynecology Unit of Arcispedale Sant’Anna of Ferrara. SFHs were collected using a tape measure, from the upper rim of the symphysis to the bottom of uterus, with patient in gynecological position.

Reasons for induction (diabetes, hypertensive disorders of pregnancy, intrahepatic cholestasis of pregnancy, oligohydramnios, intra-uterine growth restriction (IUGR)—small for gestational age (SGA), premature rupture of membranes (PROM), obesity, preventing post-maturity syndrome, other indications), Bishop’s score, body mass index (BMI), gestational age, parity, mode of induction were collected at the time of the first cycle of induction along with SFH. Number of induction cycles was also collected in the succeeding days. Time of active phase of labor was calculated as a ratio (R) between the time of initiation of partograph to time of birth (expressed in minutes) out of dilatation value (expressed in centimeters) at the time of partogram initiation. Delivery outcome (Cesarean section, operative vaginal birth, post-partum hemorrhage (PPE)), neonatal outcome (arterial cord pH, neonatal intensive care admission (NICU)), birth size (2500 g, between 2500 g and 4000 g, $\ge$4000 g) were recorded after delivery.

Intercorrelations among variables were expected. To cancel out the intercorrelations, bi-dimensional correspondence analysis (symmetrical normalization) was applied to find independent relationships among SFH classes ($\le$34 cm, 35 cm, 36 cm, 37 cm, $>$37 cm) and other variables. By plotting coordinates given by correspondence analysis for all variables in a Cartesian system, distances between the points were calculated and interpreted as independent probabilities of associations between the independent variable (classes of SFH) and other dependent variables. If distance among a SFH class point and another variable point was 0, the probability of association was 1. The highest distance between a variable point to an SFH class point was rounded to 0 and set for re-scaling all the distances as probabilities.

Probabilities were plotted according to outcome variables (upper quartile (UQ)) of R for the duration of active phase of labor, operative vaginal birth, Cesarean section, minor PPE, major PPE, arterial cord pH, neonatal intensive care (NICU) admission, two cycles of induction, three cycles of induction). Slopes were tested in regression models to find significant fit (p $\le$ 0.05). IBM SPSS statistics 27 and LibreOffice Calc 7.0 were used for the analyses.

One-hundred-sixty-nine induced pregnancies were assessed. Inductions were performed preterm, late preterm, early term, full term and late term for various indications. Table 1 describes the samples. Fig. 1 depicts the results of correspondence analysis. Red points represent the positions of SFH classes in relation with other variables (blue points). The closer a blue point is to a red point, the higher the association among the SFH class and that variable. For example, the SFH $\le$34 cm is closer to preterm delivery, meaning higher association to preterm inductions. On the other hand, SFH of 36 cm, 37 cm and over 37 cm is closer to two cycles of induction, three cycles of induction, UQ of R, operative vaginal birth, minor post-partum hemorrhage, pH $\le$ 7.15, diabetes (as the reason of induction), hypertension (as the reason of induction), both Bishop’ score $\le$3 and Bishop’ score $>$3, meaning higher association with those variables. Fig. 2 reports trends of SFH values for the outcomes variables assessed. Increased probability of adverse birth and labor outcome is observed for the SFH trends from 34 cm or less to over 37 cm. The probabilities increase over 34 cm of SFH value. Table 2 reports significance values for regression trend models for each outcome variable. The quadratic model provides the best prediction compared to other models for all outcome variables. SFH provides poor prediction for Cesarean section (significance trend reached in only the quadratic model, p = 0.027) and does not provide any prediction for the NICU admission outcome variables.

Fig. 1.

Perceptual map of two dimensional correspondence analysis. * marks the items as the reasons for induction. Variables are represented as points and grouped in two sets: the red ones (SFH classes) and the blue ones (all other variables assessed). The distances among points are reliable independent estimates of their associations. The closer is a blue dot-point to a red-dot point, the higher is the association. However, the Figure is only descriptive and it does not used for inferential insights. SFH $\le$ 34 cm is closer to preterm delivery, meaning higher association to preterm inductions. SFH of 36 cm, 37 cm and over 37 cm is closer to two cycles of induction, three cycles of induction, UQ of R, operative vaginal birth, minor post-partum hemorrhage, pH $\le$ 7.15, diabetes (as the cause of induction), hypertension (as the cause of induction), both Bishop’ score $\le$3 and Bishop’ score $>$3, meaning higher association with those variables.

Fig. 2.

Trends of birth outcomes according to SFH values. p values for each kind of trend assessed. On the y-axis probabilities are reported; on the x-axis SFH values are reported.

Findings of the present study confirm that SFH (over 34 cm) predicts adverse labor outcomes in induced pregnancies. Additionally, our study suggests that SFH is also able to predict some adverse neonatal outcomes. This study cannot assess if adverse outcomes are linked to a cause-effect relationship with gestational diseases rather than with SFH and its involvement in labor evolution. This is mainly due to communalities among each variables conditioning the outcomes. To assess the SFH association with adverse birth and neonatal outcomes, larger cohort of induced pregnancies should be analyzed, stratifying database for SFH values and comparing outcomes in multivariable models. This is hard to realize. Nevertheless, it is likely that diabetic or hypertensive patients at term with SFH below 34 cm are less likely to be at risk for adverse outcomes compared to diabetic or hypertensive patients with SFH over 34 cm for birth-size related concerns. Remarkably, the finding is poorly associated with neonatal birth weight below 2500 g or over 4000 g (Fig. 1). The results confirm that SFH cannot be used for predicting birth size [6, 7, 11, 12], leading to strengthen the hypothesis that SFH can predict the birth success [13, 14] by labor induction. Higher SFH values could be related with fetal head station, fetal head deflected positions, unstable positions and malpositions. Those can affect labor progression and onset at the beginning of induction and are not always linked with fetal birth size and Bishop’ score (Fig. 1), explaining associations with labor and birth worst outcomes.

In conclusion, SFH values could be useful for timing of induction as it links with birth and neonatal outcomes. As timing of birth is still a concern for patients with gestational diabetes, a randomized trial could be conducted to further examine the timing of induction in pregnancy affected by such a disease.

UI planned the study, analyzed data, wrote article; MGLM, BB, SC collected data and searched literature; MGLM also organized database; DM contributed to plan the study and to write article; PG supervised and gave interpretation to findings. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript.

The study was conducted in accordance with the Helsinki’ declaration and consents were obtained from the patients at the time of recovery.

We would like to express my gratitude to all those who helped me during the writing of this manuscript.

This research received no external funding.

The authors declare no conflict of interest.