Table 1.

Characteristics of included studies - Anxiety.

Study ID, country	Study design, setting, study period, type of neonatal care, length of stay	Study objective	Study inclusion criteria	Study exclusion criteria	Parents’ characteristics	Babies’ characteristics
Bonacquisti 2020, USA	Prospective cohort, 3 centres, October 2014 through May 2016, NNU level and length of stay = NR	To identify maternal psychological responses to NNU admission	Mothers ≥18 yrs, given birth less than a year ago to infants admitted to NNUs	Fathers were excluded	N = 127 mothers age = mean 29.63 yrs; living with partner = 69 (54.3%), white = 66 (52%), black = 38 (30%), nulliparous = 52 (40.9%), education (university degree and above) = 26 (20.5%), SES (unemployed) = 40 (31.5%)	N = 147, GA & BW = NR
Cajiao-Nieto 2021, Spain	Cohort study, 1 University Hospital in Barcelon, January 2016 to April 2017, NNU= level = NR, length of stay ≥15 days	To compare paternal anxiety symptoms & depression of fathers of PT babies in NNU to fathers of full term babies	Fathers could read & write in Spanish Fathers to babies in NNU for at least 2 weeks	Babies who died or transferred to another hospital	N = 51 fathers, age range 20 -> 45 yrs, all lived with partners, education (professional & superior) = 39 (76%), first-time fathers = 36 (70.2%); SES (employed) = 49 (96%), ethnicity = NR	N= NR, single birth N = 29, GA < 37 wks, BW = NR
Carter 2007, New Zealand	Prospective cohort study, 1 central: New Zealand province, Christchurch Women's Hospital, February 2001 to January 2002, NNU level III, length of stay = NR	To compare the psychosocial functioning of the parents of infants admitted to NNU with the parents of infants born at term and not admitted to the NNU	Parents of babies admitted to NNU, criteria for NNU: BW <1800 g, GA <34 wks, or any infant illness	Lack of written informed consent or knowledge that the infant would go into foster care or be adopted	N = 242 mothers, N = 205 fathers. mothers’ age = 30.1 (SD, 5.4), vs. fathers’ age 33.1 (SD, 5.9) yrs, mothers living with partner = 140 (58%), mothers’ professional qualification = 64 (52%) vs fathers: professional qualification = 50 (37%); SES = annual family income(NZ $) < $15000: 16 (7%); parity & ethnicity = NR	N = 276, mean GA = mean 35.1 (SD, 3.8) wks, range = 23-42 wks, BW = 2477 (SD, 889.1)g
Dantas 2012, Brazil	Cross-sectional, 2 hospitals, Januário Cicco Maternity School and José Pedro Bezerra and MEJC, located in the municipality of Natal, in Rio Grande do Norte (RN), April to May 2011, NNU &length of stay = NR	To identify the prevalence of symptoms of anxiety and depression in mothers of hospitalized premature infants	Mothers of preterm infants <37wks, admitted to NNU >24 hrs, age ≥18 yrs	Mothers to newborns who died, or with congenital anomaly, drug user, HIV+, mental health illness	N =70 mothers, mean age = 26.50 (range18 – 42) yrs; education: 11 (3-17) yrs; living with partner= 55 (78.6%); SES = (one salary) 17 (24.3%); occupation = 33 (47.1%); parity, SES & ethnicity = NR	N = NR, GA = mean 31.55 wks, range 26- 37 wks, BW = mean 1494g
Das 2021, USA	Cross-sectional, 1 hospital in Midwest, study period = NR, NNU level = NR, length of stay = 14-69 days	To determine whether the history of a previously diagnosed	Mothers to babies in NNU for 7–29 days	NR	N = 96 mothers, age range=22-33 yrs, white = 35 (36%), black= 49 (51%), SES = (government insurance) = 84 (88%); living with partner, education & parity = NR	N = 99, BW= 1,285- 3,112 g, GA range = 29-39 wks
Eutrope 2014a, France	Prospective cohort study, 3 hospitals-Reims, Nancy & Besancon, January 2008 to January 2010, 3B NNU (mechanical ventilation, no major surgery) or 3C NNU (major neonatal surgery, no open-heart surgery), length of stay = NR	To describe maternal feelings of delivering a premature baby	Preterm babies admitted to one of the 3 NNU, GA <32 wks	Mothers with psychiatric illness, drug or alcohol abuse, aged <18 years, language barriers; for newborns: unfavourable prognosis PRI≥ 10, significant developmental disabilities malformation and/or genetic anomaly, 30% excluded based on location	N = 100 mothers, mean age = 29.8 (SD,6.0) yrs, 92% lived with partners, higher education 79.29%, SES (employed) = 69%, nulliparous = 48%; ethnicity = NR	N = 100, multiple births = 22 twins & 4 triples; GA = mean 29.8 (SD, 6.0) wks; BW = mean 1320g
Garfield 2015a, USA	Cross-sectional, 2 hospitals inner-city medical centres serving underserved and uninsured populations, study period, NNU level & length of stay = NR	Identifying risk factors among urban, low-income mothers may enable NNU healthcare providers to more effectively screen and refer mothers with potentially elevated postpartum depressive symptom	Mothers of very low BW <1500g, preterm <37, English speaking whose infants were clinically stable	Mothers with mental health diagnosis, babies with congenital neurological problems or symptoms of substance abuse, age <18 yrs, ongoing critical illness = HIV seizure, or diagnosis of major depression, psychosis, bipolar disease. mothers of infants receiving mechanical ventilation	N = 113 mothers, mean age = 24.7 (SD, 5.17), ethnicity African- American = 81%, living with partner = 52.3%, high school graduates = 43%, SES = 39% received public aid and 40% were uninsured, parity = NR	N = NR, GA < 37 wks, BW = mean 1073 (SD, 342)g
Gonzalez-Hernandez 2019, Mexico	Cohort study, 1 centre General Hospital of Durango, May 2016 to November 2017, NICU level I, length of stay = ≥1 month	To determine the frequency of depression and anxiety in mothers to NNU babies; to provide socio-demographic characteristics of participants and variables associated with depression and anxiety	Mothers ≥15 yrs, with premature babies in NNU level I, stayed in NNU ≥1month, signed an informed consent	Mothers with a history of previous psychiatric diseases, severe medical illness, babies in NNU levels II, III or IV	N=188 mothers, mean age 24.7 years (S.D, 6.4, range 15–42) yrs, living with partner = 158 (84.0%), bachelor's degree = 9 (4.8%), SES (living in urban areas) = 103 (54.3%), parity & ethnicity = NR	N, GA & BW = NR
Greene 2015 & 2018a, USA	Prospective cohort study,1 NNU, August 2011 to December 2012, NNU-level IV, length of stay = 91 ± 37.1 [30–179] day	To examine multiple types of distress predictors of maternal NNU visitation rates and the relationships between maternal NNU visitation rates and later maternal distress and infant clinic attendance	English-speaking mothers age > 18 years, infants likely to survive assessed by the neonatologist	Congenital anomalies, drug users	N = 69 mothers, age = 26.99 (SD, 5.98) yrs, nulliparous 23 (34%), ethnicity: black = 38 (54%), non-Hispanic white = 18 (26%), Hispanic-white = 12 (17%), Asian 1 (1%); living with partners = 20 (32%), high school education = 32 (48%); SES (Public health insurance) = 44 (66%)	N = 69, GA = mean 27.5 (SD, 2.2) wks (range 23.2-32.30) wks, BW = 957 (SD, 243)g
Harris 2018a, USA	Cohort study, 2 centres Saint Louis Children's Hospital & Barnes Jewish Hospital's Special Care Nursery, January to June 2015, NNU Level III & IV length of stay = 83.4 (40.9) days	To examine the early mental health challenges in mothers of very preterm infants vs mothers of full-terms, identify family social background & infant medical factors associated with high levels of maternal psychological distress & assess the relationship between maternal psychological distress and maternal role	Mothers to infants born ≤32 weeks, free from congenital anomalies	Drug use and younger age were an exclusion criterion	N =37 mothers, age = 29.7 (SD, 6.4) yrs, multiple birth 5 (13%), SES (Low income <$25,000) = 16 (43%), college degree = 15 (41%), single 7 (19%), ethnicity = NR	N = 50, GA ≤32 wks, BW = mean 1104.0 (SD, 416.7)g
Helle 2016a, Germany	Cross-sectional, 3 largest centres of Perinatal Medical Care in Hamburg, (Altona, Barmbek, Eppendorf), study period, NNU level & length of stay = NR	investigating the prevalence of and risk for postpartum anxiety disorders, adjustment disorders and state anxiety four to six weeks postpartum in both parents with a VLBW infant compared to term infants	Mothers to very low birth infants, BW <1500g, GA<37 wks	Inability to follow study procedures, insufficient German language skills, premature discharge, residing too far from the study centre	N = 111 mothers, N = 87 fathers, mothers age = 32.6 (SD 4.66) yrs, fathers age = 23.8 (SD 7.58) yrs, nulliparous= 82 (73.9%), ethnicity = NR, living with partners = 74 (66.7%), SES (low) = 11 (10%)	N =149, GA = mean 28.2 (SD, 2.65) wks, BW = 1095.9 (SD, 330.40)g, singleton = 76 (68.5%), twin = 32 (28.8), triplet = 3 (2.7%)
Holditch-Davis 2015a, USA	Cohort design, NNUs of 4 hospitals (2 in a South-eastern state and 2 in a Midwestern state), NNU level & period = NR	To estimate the inter-correlations between depressive symptoms, state anxiety, PTS, stress due to infant appearance and behaviour, and stress due to parental role alteration in a multi-ethnic sample of m others of preterm infants during initial hospitalization	Mothers of PT babies of BW <1750g	Parents to infants, with congenital neurological anomalies, substance exposure, age< 15yrs; HIV+; psychosis/bipolar disease; depression, critical illness; non-English speaking, follow-up for 12 months was unlikely	N = 232 mothers, Age mean =27.0 yrs (SD 6.1); living with partner = 32.3%; mean education = 13.4 yrs (SD2.3); ethnicity = White = 8% Black = 69.8%, Hispanic = 8,1%, Other =1.9%. Nulliparous = 55.1%.; SES (Public assistance) =20.3%.	N = NR, mean GA=27.2 wks (SD, 2.9), mean BW = 1006.2 (SD, 326)g
Kong 2013, China	Cross sectional, 1 centre Department of Paediatrics in Nanjing Maternal and Child Health Hospital, January to September 2011, neonatal care = paediatric department, length of stay> 24 hrs	To investigate parents’ mental health of hospitalised neonates and their characteristics, to measure the stress levels and social support	Parental age ≥18 years, ability to read and write, neonates stayed in hospital >24 hours	Serious physical or mental condition	N = 600 parents, N = 200 mothers, N = 400 fathers, mothers age mean 28.53 ± 4.06 vs. fathers 30.76 ± 4.60 yrs; living with partners years = mothers 3.30 ± 3.13 vs. fathers 3.17 ±2.78 yrs; education = mothers 64% college or higher vs. fathers 73.25%; SES = mothers (low <5000 Yuan per month) 84%, vs. fathers 67.25%, ethnicity & parity = NR	N = 600, GA mean = mothers = 36.63 ± 3.34 vs fathers 37.09 ± 3.16 wks, BW mean: mothers = 2926.70 ± 937.75 vs. fathers = 3051.90 ± 1028.88g
Misund 2014 & 2016a, Norway	Prospective cohort, 1 centre at Oslo University Hospital, Norway; two periods = June 2005–January 2006 and October 2007–July 2008, NNU level & length of stay = NR	To explore the associations between maternal mental health problems following preterm birth, pregnancy and birth complications and early preterm mother–infant interaction at 6 months corrected age	Mothers of preterm babies GA <33 wks admitted to NNU	Mothers of severely ill babies that the medical staff estimated to have poor chance of survival, and non-Norwegian speakers	N = 29 mothers, at first assessment (2 wks after discharge from hospital), N=27 at second assessment (6 months corrected age) & N=26 at third assessment (18 months corrected age), mean age = 33.7 (SD, 4.3) yrs, nulliparous 18 (62.1%), education 12 years = 26 (89.7%), all living with partners, ethnicity &SES = NR	N = 35, GA median (range) = 29 (24-32)wks, mean 28.5 (SD, 2.6), BW median (range)= 1185 (623–2030) mean 1222 (SD, 423)g, multiples = twins 14 (40%) (two sets of twins were raised as singletons due to twin sibling still birth)
Mulder 2014, New Zealand	Cohort design,1 centre Christchurch Women's Hospital, NNU serving a region in central Canterbu, February 2001 to January 2002, NNU level & length of stay = NR	To evaluate the psychological functioning in parents whose infants were admitted to a NNU over the first 2 years of the infant's life	NNU admissions born to parents resident in a defined geographic area in a 12-month period were eligible for the study. Criteria for NNU admission BW <1800 g and GA<34 weeks or any illness in the infant	NR	N = 242 families, mothers N=242, mean age = 30.1(SD, 5.4), 88% living with partners, 52% professional qualification. Fathers N=205, mean age=33.1(SD,5.9), 37% professional qualification, parity = NR	GA = 23–42 wks, mean = 35.1 (SD, 3.8) wks, BW = 370–4850g, mean 2477 (SD, 889.1)g
Ong 2019, Malaysia	Prospective cohort,1 hospital, study duration 3 years, dates = NR, NNU Level III, mean length of stay = 90.5 (28.6) days	To investigate the demographics, maternal psychosocial and infant factors of mothers of very preterm infants at risk for postpartum depression/anxiety at the time of discharge from a level III (NNU)	Mothers of preterm infants born between 27 to 34 GA wks	Congenital anomaly or being moribund with severe sepsis or respiratory failure in the first days of life	N =73 mothers, mean age 27.2 (SD,7.4)yrs, high school or less =4 6.5%, living with partner = 42.5%, SES (public insurance) = 69%, nulliparous 34.3%, SES = NR	N =73 infants, mean GA =26 wks (SD, 1.8), 27-34 wks BW = NR
Onay 2021, Turkey	Cross-sectional, 1 hospital, Eskisehir Osmangazi University Hospital, November 1, 2018 and February 1, 2020, NNU – level III; length of stay ≥7 days	To investigate the relation between breastfeeding exclusivity of NNU infants and the severity of anxiety and depressive symptoms of NNU mothers in early postpartum period	Mothers to preterm and term infants admitted to the NNU	Mothers < 18 years, cannot give breast milk not speaking Turkish, for babies with congenital/ chromosomal abnormalities, inherited metabolic diseases, <7 days NNU, babies who died	N = 93 mothers, mean age = 30.61 yrs, living with partner = 91 (97.8%), education (university)= 26 (28.0%), SES (unemployed) = 68 (73.1), nulliparous = 38 (40.9%), ethnicity = NR	N = 105, GA ≤32 wks = 28 (26.7%), 32–36 wks = 47 (44.8%), > 37 wks = 30 (28.5), BW ≤2,500g = 64 (61%), >2,500g = 41 (39%)
Pace 2016a, Australia	Prospective cohort, 1 centre at Royal Women's Hospital, Melbourne, January 2011 to December 2013, NNU level & Length of stay = NR	To describe the trajectory and predictors of distress in parents of very preterm infants during the first 12 weeks after birth, to compare rates of depression and anxiety in parents of very preterm to term	Families with very preterm infants, GA <30 wks admitted to NNU	Parents who did not speak English, infants with congenital abnormalities, unlikely to survive according to the attending medical team	N= 113 mothers and 101 fathers, mothers age: mean (SD) = 32.7 (5.3) yrs vs. fathers 34.7 (SD, 6.4) yrs, higher social risk all sample= 43%, ethnicity& relationship = NR	N =150 (31 twins, 1 set triplets, 6 died) GA = mean 27.7 (SD, 1.5)wks, BW = mean = 1021(SD, 261)g, Singleton birth = 84 (56%)
Rogers 2013, USA	Prospective cohort,1 hospital, 3 year-period, level III urban NNU, length of stay = mean 90.5 (28.6) days	To assess factors for identifying mothers at-risk for postpartum depression or anxiety at the time of NNU discharge among Caucasian and African-American mothers	Mothers to preterm infants born <30 wks	Mothers to babies with congenital anomaly or being moribund with severe sepsis or respiratory failure in the first days of life	N = 73 mothers, age = 27.2 (SD, 7.4) yrs, nulliparous = 34.3%, living with partner= 42.5%, high school or less = 46.5%, SES (public insurance) = 69% Caucasian vs. African American= N=36 vs 37, age 29.5 (SD, .82) vs.25 (5.9) yrs, nulliparous = 34% vs.34.3, living with partner= 73.5% vs. 10.88%,high school or less =37.1 % vs. 55.6%, public insurance 50% vs. 86.5%	N= 73 infants, GA = mean 25.5 (1.8) wks, BW = NR
Segre 2014 & McCabe-Beane 2018, USA	Cross-sectional, 1 centre Midwestern academic medical center; December 2010 to May 2012, Level IV NNU, length of stay = NR	To determine whether a diagnostic classification approach or a common-factor model better explained the pattern of symptoms reported by NNU mothers and risk factors of aversive emotional states in NNU mothers based on the supported conceptual model and to expand depression screening to include anxiety symptoms	Mothers to NNU babies, >18 years of age, and English speaking	NR	N = 200 mothers, mean age = 28.1 (SD, 5.7) yrs, ethnicity = Caucasian = 178 (89.9%), African American = 12 (6.1%), living with partners = 123 (61.8%), education = mean 14.6 (SD, 2.5) yrs SES (employed) = 132 (66.3%) & income > $50,000 = 83 (45%), parity= NR	N = NR, BW = 397- 4,706g, GA= 23-41 wks
Trumello 2019, Italy	Cohort prospective,1 centre Chieti University Hospital, NNU, study period & length of stay = NR	To explore psychological functioning and mental representations in mothers of preterm infants during NNU stay	Mothers to babies < 37 wks, mother's age ≥18 yrs, mother's good knowledge of the Italian language, and absence of mother's drug or alcohol addiction	Babies genetic illnesses, neonatal deformities, and neurological damages clinically identifiable at birth	N = 62 mothers, mean age 33.98 (SD, 4.76) yrs, all white, SES (middle) = 79%, parents lived together = 59 (95%), employed = 50 (80.6%), nulliparous = 43 (69.4%), university = 20 (31.8%)	N = NR, GA <32 wks = 40 (35.5%), ≥32 wks = 22 (64.5%), BW = mean 1685.42 (SD, 525.4)g

Abbreviations: NR: Not reported; BW: Birth weight; wks: Weeks; hrs: Hours, yrs: Years, GA: Gestational age; NICU: Neonatal intensive care unit, PRI: Perinatal risk inventory; SES: Socioeconomic status, HIV: Human immunodeficiency virus, SD: Standard deviation

^aStudies included in both anxiety and PTS