In this study, we observed that adolescent mothers were more likely to have an infant with the adverse birth outcome of preterm delivery, LBW, ENND, or a major external birth defect such as gastroschisis as compared to mothers 20-34 years. Previous studies have also found an increased risk for preterm delivery in adolescent births,[7, 14, 19] which could be attributable to the maternal-fetal competition for nutrients that arises when pregnancy coincides with continuing or incomplete growth in adolescents. Our study finds that adolescent mothers were more likely to deliver LBW babies, and is consistent with results from the Uganda Demographic Health Survey (UDHS) 2011,  and several other studies in sub-Saharan Africa. [14, 34-36] That UDHS also identified infants born with LBW to be at increased risk of neonatal death, highlighting the risks associated with LBW in this population. The LBW observed among infants born to adolescent mothers could have been due to factors such as inadequate maternal nutrition, or the related but distinct issue of inadequate weight gain during pregnancy, which were not assessed in our study.
Comparable to findings from a study exploring the impact of early motherhood on neonatal mortality in 45 low and middle-income countries,  our study showed that ENNDs in full-term babies occurred more frequently among adolescent mothers. In contrast, a World Health Organization (WHO) multi-country survey across 29 countries in Africa, Asia, Latin America, and the Middle East found that ENND among infants born to adolescent mothers was not significantly different from mothers aged 20-24 years, after adjustment for gestational age and birth weight. This difference may be related to restriction in the WHO study to mothers aged 24 years or younger who gave birth to an infant of at least 22 weeks’ gestation as compared to mothers ≤34 years in our analysis, and the WHO study’s classification of ENND as intra-hospital deaths that occurred within 7 days after birth as compared to deaths within 48 hours in our analysis.
In this study, adolescent mothers were more likely to deliver a newborn with a birth defect when compared with mothers 20-34 years. These findings are consistent with findings from studies in North America and Europe.[38, 39] Our finding of a higher birth defects prevalence estimate (per 10,000 births) among adolescent mothers compared to older mothers is consistent with findings from a population-based prevalence study using data from EUROCAT congenital anomaly registers in 23 regions of Europe in 15 countries. However, Zile and Villerusa et al. (2013), from a study based on data from the Medical Birth Register in Latvia differed showing that the prevalence of birth defects was instead higher for mothers aged 20–34 years as compared to adolescent mothers. The difference could however be attributed to the fact that our study’s prevalence estimates included births from all live births, stillbirths, and spontaneous abortions while Zile and Villerusa et al. (2013) included only live births and also included other defects/syndromes and chromosomal defects.
Although the number for some birth defects were small in our study, our findings suggest that(32) gastroschisis was significantly higher among adolescent mothers when compared to mothers 20-34 years. The strong association between adolescents births with gastroschisis has also been reported by other studies.[28, 38, 39, 41] While comparing gastroschisis to other congenital anomalies, Given, et al. (2017) reported sexually transmitted infections, and continuation of oral contraceptives in early pregnancy, as preventable risk factors. However, we were not able to assess these factors in this study.
Our study also found that adolescent mothers were associated with increased odds of musculoskeletal defects as well as malformations of eyes and ears combined. In one retrospective cohort study in the United States of America,  Chen, et al. (2007) found increased odds of musculoskeletal defects, however, the study included some other defects within the category, specifically, polydactyly/syndactyly/adactyly, diaphragmatic hernia, integumentary anomalies.
We also found that a significantly higher proportion of HIV-infected adolescents were not on ART at conception or delivery compared to women 20-34 years, which is consistent with findings from the Uganda Population-Based HIV Impact Household-based National Survey. Maternal HIV infection has been shown to be associated with increased rates of adverse pregnancy outcomes such as LBW, prematurity, and ENND , and the lower prevalence of ART use among HIV-infected adolescents would further exacerbate the situation because it translates to a potential increased risk of MTCT of HIV among adolescents compared to mothers (20-34 years) justifying the need to strengthen services for this population. 
STUDY STRENGTHS AND LIMITATIONS
This study’s strengths include a large sample size, which made it possible to assess the association between adolescent births and possible risk factors of adverse birth outcomes. In addition, our study used an active birth defects case ascertainment and collection of data to ensure accuracy and improved birth defect detection and reporting versus extraction of data from medical records. Also, the physical examination of newborns by trained staff and several levels of external birth defect review ensured consistent birth defect classification and coding.
Unlike other studies that only include live births,[38, 40] this study included stillbirths, spontaneous abortions, and live births which minimized selection bias especially since some structural birth defects commonly occur among stillbirths thereby giving more accurate risks and birth prevalence estimates among the different age groups.
Study limitations include surveillance activities being conducted at four major urban hospitals located in the capital city and is not representative of adolescent births nationally. However, since 55% of the births in Kampala were at these four hospitals, and one of them (Mulago National Referral Hospital) contributed 60.0% of the total births,  they provide a fair representation of births nationally. Secondly, because infants were not followed post-discharge, we captured only ENND that occurred within 48 hours of birth. The standard definition of ENND is death within seven days of delivery so infants that died between discharge and seven days of life was not accounted for, resulting in a possible underestimation of ENND.
In addition, this study did not control for several risk factors known to influence reproductive health outcomes such as social-economic status, level of education, tobacco smoking, alcohol drinking, maternal nutrition, and the use of folic acid since this information was not captured in the surveillance. [28, 46]
Finally, it has been demonstrated that adolescents are not a homogeneous group, and therefore differ in their emotional or cognitive development,  and that categorizing adolescents into one age group could withhold full knowledge of the most vulnerable age groups associated with adverse birth outcomes. However, we lumped the adolescent age-group into one group of mothers less than 19 years of age because our study had small segregated sample sizes within the finer age group categories, especially in the 12-14-year-old group. Therefore, further research from this ongoing surveillance will seek to investigate the risk factors associated with the different adolescent age groups.