Keywords teenage pregnancies - adolescence - pregnancy outcome - Austria - risk factors
Introduction
According to the World Health Organization (WHO), around 16 million girls between 15 and 19 years of age give birth every year [1 ]. From
an international perspective, complications in the context of pregnancy and childbirth are the most common cause of death in adolescent girls [1 ]
[2 ]
The WHO defines adolescence as the period from childhood to adulthood between 10 and 19 years of age [3 ]. Teenagers are young people from
13 to 19 years of age.
Although the highest number of teenage pregnancies occur in low-income countries, the causes and consequences of such pregnancies are of increasing scientific and political interest in
high-income countries [4 ]. According to the European Perinatal Health Report 2015, Switzerland with 0.8% was the European country with the
lowest rate of pregnant women under 20 years of age, the highest rate was recorded with 10.2% in Bulgaria [5 ]. In 2018, 1.3% of all
pregnant women in Finland and 9.1% in Romania delivered between 15 and 19 years of age [6 ]. There has been a steady decline in the number
of teenage pregnancies throughout Europe since 2001 [7 ]. Between 2012 and 2020, the number of deliveries among young women under the age
of 20 almost halved in Austria, from 2.6% of all deliveries in 2012 to 1.3% in 2020 [8 ].
The most common causes of teenage pregnancies include poverty and a low level of education as well as early marriage, lack of sex education and the lack of availability of effective
contraceptives [1 ]
[2 ]
[4 ]
[9 ]
[10 ].
In addition to social effects, pregnancies in adolescence are associated with increased maternal, obstetric and neonatal risks [1 ]
[2 ]
[9 ]
[11 ]
[12 ]
[13 ]
[14 ]
[15 ]. However, deliveries of teenage mothers show significantly lower rates of caesarean sections and operative vaginal births [2 ]
[16 ].
The literature reports higher preterm birth rates, lower birth weights and increased neonatal mortality in adolescent mothers [1 ]
[12 ]
[13 ]
[14 ]
[17 ]. In addition, an association was found between low 5-minute Apgar scores of newborns and young maternal age [13 ]
[14 ]
[15 ]. An increased
incidence of hypertensive pregnancy disease in teenagers is discussed in some papers, but the data on this issue is inconsistent [12 ]
[14 ]
[18 ].
Furthermore, teenagers are at increased risk of acquiring sexually transmitted infections, which may lead to possible obstetric complications such as preterm premature rupture of the
membranes (PPROM) with a signficantly increased risk for preterm birth, triple I and/or postpartum infections [2 ]
[16 ]. The use of nicotine, alcohol or drugs during pregnancy is also observed more frequently in adolescent pregnant women than in adults [2 ]
[13 ].
Most adolescent pregnancies are unplanned [1 ]
[7 ]
[13 ]
[16 ]. In order to fully consider the number of teenage pregnancies, the rate of
abortions in teenagers must also be discussed in more detail [7 ]. Mostly, live birth rates are fully recorded worldwide. However, the rate
of termination of pregnancy is only recorded in a few countries and the unreported number of illegal abortions also plays a pivotal role. In Austria there is unfortunately no complete
information on the number of abortions [4 ].
The aim of this retrospective cohort study is to investigate the frequency of teenage pregnancy and the differences between teenage and adult pregnancies in Austria (between 01/2012–12/2020)
with regard to relevant obstetric outcomes. Based on the existing data, the hypothesis for this study was, that within the study collective significant differences in neonatal outcome,
delivery and preterm birth rates between both groups can be found.
Material and Methods
Austrian register of deliveries
In order to evaluate the frequency and obstetric outcome of teenage pregnancies in Austria, an application for special evaluation was submitted to the Austrian Register of Deliveries
(Geburtenregister Österreich [GRÖ]). This register collects data on obstetric events in hospitals throughout Austria. The rights and obligations of the GRÖ are agreed in a contract between
the clinic/department and the Institute for Clinical Epidemiology of the Tirol-Kliniken. In order to warrant data security, data of clinics/departments are only submitted in pseudonymized
form (indirect personal data) to the GRÖ [19 ].
Data of 751661 births and 11809 deliveries of teenagers in Austria within the period 01/2012 to 12/2020 were available for data evaluation.
Inclusion and exclusion criteria
Included were only 372502 primiparous, while 345174 multiparous women were excluded. The mothers were divided into two age categories: 10562 mothers ≤ 19 years and 361940 older 20 to 39
years. 33711 pregnant women aged 40 years and over were excluded (see [Fig. 1 ]).
Fig. 1 Flow chart of included and excluded deliveries.
Statistical analysis
Statistical analysis was performed by the GRÖ. Qualitative data are given as absolute (n) and relative (%) frequencies. Quantitative data are presented as median (interquartile range). The
study groups were compared by using chi-square test (qualitative data) and Mann-Whitney U test (quantitative data, 2 groups). P values < 0.05 were considered statistically significant.
All statistical analyses were performed using STATA 13 (StataCorp. 2013. Stata Statistical Software: Release 13. College Station, TX: StataCorp LP.).
Ethics committee opinion
A positive vote (1301/2020) of the Ethics Committee of the Johannes Kepler University Linz was obtained before the start of the study.
Results
Frequency of pregnancies in Austrian teenagers
During evaluation period 751661 deliveries in Austria were recorded, of which 11809 were girls under 20 years of age. 49 deliveries were reported for girls in early adolescence (10 to 14
years of age). This corresponds to a rate of 1.6% teenage pregnancies during the observation period. Since none of the mothers was younger than 13 years of age, the terms teenagers and
adolescents can be used synonymously in this cohort.
10562 (89%) of parturients under 20 years of age were primiparous.
The parameters collected from the register are summarized in [Table 1 ], [Table 2 ], [Table 3 ], [Table 4 ].
Table 1
Maternal characteristics according to age category (IQR = Interquartile Range; BMI = Body Mass Index; SD = Standard
Deviation).
≤ 19 years
(n = 10562)
19–39 years
(n = 361940)
P value
Age (years) (mean, SD)
18.1 ± 1.1
29.3 ± 4.6
< 0.001
Weight (kg) (mean, SD)
60.8 ± 13.2
65.0 ± 13.6
< 0.001
Height (cm) (mean, SD)
164.0 ± 6.4
166.3 ± 6.2
< 0.001
BMI (kg/m2 ) at the beginning of pregnancy (mean, SD)
22.5 ± 4.5
23.5 ± 4.6
< 0.001
Maternal obesity (n, %)
628 (6.9%)
28 348 (9.1%)
< 0.001
Gestational diabetes (n, %)
255 (2.4%)
14323 (4.0%)
< 0.001
Smoking during pregnancy (n, %)
2321 (22.7%)
20551 (5.7%)
< 0.001
Maternal mortality (n, %)
0 (0%)
16 (0.00004%)
0.494
Table 2
Neonatal outcome according to age category (IQR = Interquartile Range; NICU = Neonatal Intensive Care Unit; SD = Standard
Deviation).
≤ 19 years
(n = 10562)
19–39 years
(n = 361940)
P value
Birthweight (g) (mean, SD)
3216 ± 564
3247 ± 576
< 0.001
Height (cm) (mean, SD)
49.98 ± 3.11
50.31 ± 3.16
< 0.001
Weight ≤ 3rd percentile (n, %)
504 (4.8%)
12835 (3.6%)
< 0.001
Weight ≥ 97th percentile (n, %)
625 (6.0%)
26590 (7.4%)
< 0.001
Arterial umbilical cord pH (mean, SD)
7.25 ± 0.08
7.26 ± 0.08
< 0.001
Venous umbilical cord pH (mean, SD)
7.31 ± 0.07
7.32 ± 0.08
< 0.001
Arterial cord pH < 7.0 (n, %)
38 (0.37%)
1316 (0.38%)
0.940
Apgar 1-minute (mean, SD)
8.72 ± 1.30
8.74 ± 1.23
0.017
Apgar 5-minute (mean, SD)
9.66 ± 1.06
9.67 ± 0.97
< 0.001
Apgar 10-minute (mean, SD)
9.83 ± 0.90
9.85 ± 0.81
0.265
5-minute Apgar < 4 (n, %)
79 (0.75%)
1958 (0.54%)
0.004
5-minute Apgar < 7 (n, %)
186 (1.77%)
4937 (1.37%)
0.001
Transfer to NICU (n, %)
852 (8.1%)
28364 (7.8%)
0.386
Neonatal mortality (n, %)
75 (0.7%)
2029 (0.6%)
0.043
Table 3
Delivery according to age category (IQR = Interquartile Range; SD = Standard Deviation; WoP = Week of Pregnancy).
≤ 19 years
(n = 10562)
19–39 years
(n = 361940)
P value
WoP at delivery (mean, SD)
38.8 ± 2.2
38.8 ± 2.2
0.170
Induction of labor (n, %)
2445 (23.1%)
82674 (22.8%)
0.459
Premature rupture of membranes (PROM) (n, %)
2518 (23.8%)
105119 (29.0%)
< 0.001
Caesarean section rates (primary and secondary) (n, %)
1557 (21.1%)
114990 (31.8%)
< 0.001
Operative vaginal birth (n, %)
923 (8.7%)
42196 (11.7%)
< 0.001
Episiotomy (n, %)
1590 (15.1%)
59385 (16.4%)
< 0.001
Perineal tear III or IV (n, %)
135 (1.3%)
7677 (2.1%)
< 0.001
Multiples (n, %)
149 (1.4%)
12044 (3.3%)
< 0.001
Table 4
Preterm birth rates and birth weight according to age category (SD = standard deviation).
Preterm birth rates
Birth weight (g) per subgroup (mean, SD)
≤ 19 years
(n, %)
19–39 years
(n, %)
P value
≤ 19 years
19–39 years
P value
Total preterm births
913 (8.7%)
32873 (9.2%)
0.111
Border of viability
15 (0.14%)
453 (0.13%)
0.618
495 ± 118
565 ± 206
0.037
Extreme preterm birth
52 (0.5%)
1641 (0.45%)
0.537
859 ± 270
818 ± 225
0.382
Very preterm birth
104 (0.99%)
3610 (1.0%)
0.931
1369 ± 370
1388 ± 336
0.440
Moderate preterm birth
110 (1.05%)
4464 (1.24%)
0.085
1881 ± 329
1907 ± 350
0.677
Mild preterm birth
632 (6.02%)
22705 (6.29%)
0.271
2586 ± 458
2527 ± 424
0.002
Maternal characteristics
The mothers in the age group ≤ 19 years were on average 18.1 ± 1.1 years old and the mothers in the group of 20 to 39 29.3 ± 4.6 years old (p < 0.001).
The mean body weight at the beginning of pregnancy was significantly lower in the under-20-year-old group (60.8 ± 13.2 vs. 65.0 ± 13.6 kg, p < 0.001). The teenage pregnant women had a
lower body height (164.0 ± 6.4 vs. 166.3 ± 6.2 cm, p < 0.001) and a lower body mass index (BMI) at the beginning of pregnancy (22.5 ± 4.5 vs. 23.5 ± 4.6 kg/m2 ,
p < 0.001).
The rate of obesity (defined as BMI ≥30 kg/m2 ) was 6.9% in the teenage mother group and 9.1% in the adult group (p < 0.001).
The number of women with gestational diabetes was also higher in the age category over 20 years than in young mothers (2.4 vs. 4.0%, p < 0.001). Among teenagers were significantly more
smokers (22.7 vs. 5.7%, p < 0.001). No difference was found in peripartum maternal mortality (0% vs. 0.00004%, p = 0.494).
The maternal characteristics according to age groups are shown in [Table 1 ].
Neonatal outcome
The neonates of pregnant women under 20 years of age had a lower birth weight (3216 ± 564 vs. 3247 ± 576 g, p < 0.001) and a shorter body length (49.98 ± 3.11 vs. 50.31 ± 3.16 cm,
p < 0.001).
In addition, the newborns of teenage mothers were more often at or below the 3rd percentile concerning birthweight (4.8 vs. 3.6%, p < 0.001). The birthweight of children from adult
mothers was significantly more often equal or greater than the 97th percentile (6.0 vs. 7.4%, p < 0.001).
The postpartum pH values in the umbilical cord artery were significantly lower in the newborns of mothers under 20 years of age than in those of adult mothers (7.25 ± 0.08 vs. 7.26 ± 0.08,
p < 0.001). The venous umbilical cord pH values were also lower in teenage mothers (7.31 ± 0.07 vs. 7.32 ± 0.08, p < 0.001). Concerning the rate of severe fetal acidosis (arterial
umbilical cord pH < 7.0), there was no significant difference between the two groups (0.37 vs. 0.38%, p = 0.940).
The Apgar scores of neonates from young mothers were significantly lower after 1 and 5 minutes, the Apgar score after 10 minutes did not differ significantly (Apgar 1-minute 8.72 ± 1.30 vs.
8.74 ± 1.23, p = 0.017; Apgar 5-minute 9.66 ± 1.06 vs. 9.67 ± 0.97, p < 0.001; Apgar 10-minute 9.83 ± 0.90 vs. 9.85 ± 0.81, p = 0.265).
The newborns of teenage mothers had significantly higher rates of very low (< 4) and low (< 7) Apgar scores after 5 minutes (5-minute Apgar < 4: 0.75 vs. 0.54%, p = 0.004)
(5-minute Apgar < 7: 1.77 vs. 1.37%, p = 0.001).
There was no difference in the frequency of transfers to the neonatal intensive care unit (NICU) (8.1 vs. 7.8%, p = 0.386). However, neonatal mortality was significantly higher in the group
of teenage mothers (0.7 vs. 0.6%, p = 0.043).
Neonatal outcome data according to age groups are summarized in [Table 2 ].
Delivery
There was no difference in the week of pregnancy (WoP) at delivery (38.8 ± 2.2 vs. 38.8 ± 2.2 WoP, p = 0.170). Induction of labor was equally frequent performed in both age groups (23.1 vs.
22.8%, p = 0.459). Premature rupture of the membranes (PROM) occurred significantly more frequently in adult mothers (23.8 vs. 29.0%, p < 0.001).
The rate of primary and secondary Caesarean sections (21.1 vs. 31.8%, p < 0.001) and the percentage of operative vaginal births (8.7% vs. 11.7%, p < 0.001) was significantly lower in
young mothers than in adult mothers. In teenagers, episiotomy was performed less frequently (15.1% vs. 16.4%, p < 0.001) and there were fewer higher-grade perineal tears (Grade III and IV
perineal tears) (1.3 vs. 2.1%, p < 0.001). Significantly more deliveries of multiples were recorded in adult pregnant women (p < 0.001). Among the teenagers, there were 146 twin births
(1.38%) and 3 deliveries of triplets (0.03%). Among adult women, 11681 twins (3.23%), 347 triplets (0.1%) and 16 quadruplets (0.004%) were recorded.
Delivery outcome data according to age groups are highlighted in [Table 3 ].
Preterm birth rates
The rate of preterm birth < 37+0 WoP was not significantly different in the group of teenage mothers compared to adult mothers (8.7 vs. 9.2%, p = 0.111). Additionally, a subgroup
analysis regarding WoP at delivery was performed (see [Table 4 ]). According to international standards preterm birth was classified into
following categories: border of viability (22+0 – 23+6 WoP), extremely preterm (24+0 – 27+6 WoP), very early preterm (28+0 – 31+6 WoP), moderately preterm (32+0 – 33+6 WoP) and mildly
preterm (34+0 – 36+6 WoP).
No significant difference between teenagers and adult mothers was found in the frequency of preterm births within individual subcategories.
In addition, birthweight was compared in relation to WoP at delivery with the aim to minimize the influence of gestational age at birth. The newborns of young mothers born at the border of
viability or mildly preterm had significantly lower birthweights than neonates from mothers between 20 and 39 years of age (border of fetal viability: 495 ± 118 vs. 565 ± 206 g, p = 0.037;
mild preterm birth: 2586 ± 458 vs. 2527 ± 424 g, p = 0.002). No significant difference was found in the other categories (extreme preterm birth: 859 ± 270 vs. 818 ± 225, p = 0.382; very
early preterm birth: 1369 ± 370 vs. 1388 ± 336, p = 0.440; moderate preterm birth: 1881 ± 329 vs. 1907 ± 350, p = 0.677).
Discussion
Despite declining rates in recent years, teenage pregnancies are a considerable obstetrical issue in Western countries and thus also in Austria. However, currently there are no evidence-based
recommendations and/or guidelines for obstetric care of this important patient group.
The available data show that adolescent pregnant women have a lower height and body weight and a lower body mass index than adult pregnant women. This is accompanied by a significantly lower
incidence of gestational diabetes and maternal obesity in younger pregnant women.
The proportion of smokers among teenagers is over 22% and more than three times higher than that of adult pregnant women. This high discrepancy in concerns of smoking status between both
groups could also be a possible selection bias as asking for risk factors in pregnant adolescents is probably more detailed during anamnesis. A documented rate of 5.7% smokers among adult
pregnant women seems relatively low. According to the European Perinatal Health Report 2015, the rate of pregnant women with nicotine abuse in Europe was between 3.6% in Norway and 16.3% in
France [5 ]. A total of 17.8% of all Austrian women reported smoking cigarettes in 2019 [20 ].
The birthweight and body length of the newborns of teenage mothers are significantly lower. The birthweight of neonates from teenage mothers is significantly more often at or below the 3rd
percentile, while the birthweight of newborns from adult mothers is more frequently equal or higher than the 97th percentile. The lower birthweights and percentiles among neonates of teenage
mothers might be explained by the physical constitution in concerns of partly unfinished body growth of adolescents. In the literature, the increased nutrient requirement of growing mothers
and thus a kind of competition for nutrients with the fetus is discussed as a possible pathogenesis [15 ]
[18 ].
The relationship between fetal macrosomia and gestational diabetes is clearly demonstrated in studies and guidelines [21 ]
[22 ]. In the present study collective the birthweigth of newborns from mothers with gestational diabetes also tends to be higher. The lower
percentage of mothers with gestational diabetes in the teenager group might be another reason for lower birthweights. Another explanation could be the higher rate of nicotine abuse in the
group of pregnant teenagers. The relationship between smoking during pregnancy and low birthweight is also known [5 ]
[23 ]
[24 ].
Remarkable are the differences in neonatal umbilical cord pH values and Apgar scores with significantly lower Apgar scores after 1 and 5 minutes in the teenager group and higher rates of low
(< 7) and very low (< 4) Apgar scores after 5 minutes. Lower Apgar scores in adolescent mothers have also been found in other studies, but the cause for this association remains unclear
[13 ]. In the literature, an association between the level of maternal education and low Apgar scores is discussed [25 ]. In addition, both low child weight and inadequate prenatal screening examinations are considered risk factors for low Apgar scores in
adolescent mothers [26 ]. No difference in the rate of transfers to the NICU was found in the available data. However, neonatal mortality
was significantly higher in mothers under 20 years of age than in adult mothers. These results are in line with international studies [15 ].
The high rate of above-mentioned obstetric complications compared to adult mothers might be explained by the fact that pregnant teenagers consult their health care provider for screening
examinations less frequently or late during pregnancy [2 ]
[12 ]
[27 ]. Studies have shown that these prenatal examinations significantly improve pregnancy outcome, especially in adolescent mothers [16 ]
[27 ]. Late sonographic examinations during pregnancy, especially after the 23rd WoP,
can be misleading for calculation of the delivery due date. Pregnancies with an unclear due date are known to be associated with a worse obstetric outcome [28 ]. Variables such as performed screening examinations or ambiguity concerning due dates are not recorded in the GRÖ and thus represent a
possible bias with regard to the poorer outcome in adolescent mothers.
In the present collective, no increased rate of preterm births could be found in teenage mothers, although according to the literature maternal age below 18 years was found to be a risk
factor for preterm birth [17 ]. The analysis of the various classes of preterm births, ranging from border of viability to mild preterm
births, also shows no significant difference between young and adult mothers.
However, it should be emphasized that in the present collective, the birthweight at the border of viability (22+0 – 23+6 WoP) in the cohort of teenage mothers was significantly lower than in
the newborns of adult mothers (495 ± 118 vs. 565 ± 206 g, p = 0.037). In perinatal and neonatal counselling of mothers with threatened preterm birth in this critical phase of pregnancy
estimated fetal weight is a fundamental parameter to calculate the probabilities for neonatal survival and morbidity, which significantly influences the decision to/or not to initiate
provisional care. In addition to the WoP, various prognostic tools also implicate estimated fetal weight for risk calculation. One of these tools is the National Institutes of Health (NIH)
Extremely Preterm Birth Outcomes Tool, which makes it possible to assess the perinatal outcome, in particular the average chance of survival and the risk of neurological impairments [29 ]. For example, when calculating the average survival for a female fetus in the completed 23rd WoP after a full course of antenatal
corticosteroids and with an estimated fetal weight of 495 g (average weight of newborns in the teenager group), the probability for survival would be 43%. In a fetus under the same conditions
and an estimated weight of 565 g (average weight of newborns in the adult mother group), the average survival would be 50% and thus significantly higher [30 ].
Therefore, it is essential to consider possible differences in children's weight when counselling pregnant teenagers in that situation. If weight limits are drawn for all pregnant women
regardless of maternal age, this will lead to incorrect judgements in counselling of adolescent mothers as constitutional weight differences are neglected. Furthermore, data from existing
literature show that the expertise of the maternity clinic in concerns of preterm birth has a significant effect on the delivery outcome [29 ]. Due to the less frequent or late pregnancy screening examinations of teenage pregnant women [2 ]
[12 ]
[27 ], an immediate transfer of teenage mothers with threatened preterm birth to a
perinatal center with high level expertise is mandatory.
Contrary to various international studies [2 ]
[16 ], no increased occurrence of PROM
in pregnant teenagers was found in this cohort. This might be explained by the fact that screening examinations for infections are part of the Austrian mother-child passport (Mutter-Kind-Pass)
and thus vaginal infections as possible triggers for PROM might be recognized in earlier stages and, if necessary, adequately treated.
The caesarean section rate in the under-20 age group was significantly lower than for women over 20 years of age. In the younger age group, the rate of caesarean sections was about a third
lower. The literature confirms a lower caesarean section rate in teenage mothers and an increasing rate of caesarean sections with a higher maternal age [2 ]
[16 ]
[31 ]. This might be due to the lower percentage of
macrosomia and the rarer use of oxytocin during childbirth in adolescent mothers [32 ]. In older pregnant women, the contractility of the
myometrium and the number of oxytocin receptors decrease, which is associated with a higher rate of caesarean sections [31 ]
[33 ].
The significantly lower rate of operative vaginal births in the group of younger mothers (8.7%) compared to adult mothers (11.7%) overlaps with data from international studies [2 ]. In mothers under the age of 20, episiotomy was performed less frequently during delivery and the rate of higher-grade perineal tears was
lower. This could possibly be related to the lower rate of operative vaginal births in teenage mothers, since in practice an episiotomy, especially in the presence of pathological CTGs, is
frequently performed during vacuum extraction. Whether a routine episiotomy reduces the rate of higher-grade birth injuries during operative vaginal births is considered controversial and is
not clearly evident from the literature [34 ]. Moreover, the newborns of teenage mothers were significantly lighter and smaller. This
could also explain the lower rate of higher-grade perineal tears, episiotomies and operative vaginal births.
A strength of this study is the large number of cases, which results in statistical significances even in parameters with only small differences, such as neonatal pH values and Apgar scores.
Limitations of this study are the retrospective design and incomplete/missing documentation of relevant pregnancy risks, such as hypertensive pregnancy disorders, number of
abortions/terminations of pregnancy and timepoints of pregnancy screening examinations, within the GRÖ. In addition, the quality of data in register studies is dependent on numerous variables,
such as the accuracy and completeness of data inputs. Furthermore, the influence of socioeconomic factors in teenage pregnancies cannot be verified due to the lack of documentation in the GRÖ,
which can be considered a potential bias of the results.
Conclusion
The data of this study highlight that pregnancy and delivery in teenage mothers need to be considered differently than in adults. A lower birth weight in newborns of teenage mothers, as well
as a significantly lower caesarean section rate, confirm the data from the existing literature. Prenatal and peripartum care of these young mothers needs to be optimized in order to reduce
worse neonatal outcomes, such as lower Apgar scores/pH values and infant mortality, in the future. Particular causes for these worse outcomes in teenage mothers remain unclear and should be
subject of future investigations.
Moreover, further studies are needed to shed more light on pregnancy risks, such as hypertensive pregnancy disorders or socioeconomic effects of pregnancies in Austrian teenagers.
Furthermore, obstetricians should be supported by evidence-based recommendations and/or guidelines in regards of pregnancy care in teenage mothers.
