Instabilities of rotating inclined buoyancy layers

The boundary layer near a cooled inclined plate, which is immersed in a stably stratified fluid rotating about an axis parallel to the direction of gravity, is a model for katabatic flows at high latitudes. In this paper the base flow of such an inclined buoyancy layer is solved analytically for arbitrary Prandtl numbers. By applying linear stability analyses, five unstable modes are identified for both the fixed temperature and the isoflux boundary conditions, i.e., the stationary longitudinal roll (LR) mode, the oblique roll with low streamwise wave-number (OR-1) and high streamwise wave-number (OR-2) modes, and the Tolmien-Schlichting (TS) wave with low streamwise wave-number (TS-1) and high streamwise wave-number (TS-2) modes. It is indicated that the Coriolis effect induced by the rotation leads the critical modes to be three dimensional, and a larger tilt angle of the plate and stronger Coriolis effect cause both TS wave modes to be more unstable for both thermal boundary conditions. When the Coriolis effect is considered, the OR-1 and OR-2 modes are the most unstable mode at low and high tilt angles, respectively, but the TS-1 wave mode may be the most unstable one when the plate is nearly vertical. In addition, the spanwise phase velocities of the TS wave modes change directions as the tilt angle passes some threshold values for both thermal boundary conditions except for the TS-1 wave mode with a fixed temperature boundary condition, which propagates in the same spanwise direction for all explored tilt angles.

A178 BIOLOGIC THERAPY DURING PREGNANCY AS PER GUIDELINE RECOMMENDATIONS REDUCES ADVERSE PREGNANCY RELATED OUTCOMES

Background

Inflammatory bowel disease (IBD) disease activity during pregnancy is associated with adverse neonatal and pregnancy-related outcomes. Biologics are used to suppress disease activity but crosses the placenta in the third trimester. Conflicting studies and guidelines on the timing of biologic dosing in pregnancy persist as we try to balance the risk of disease flare and possible adverse drug effects. The American Gastroenterology Association (AGA) recommends timing the final dose according to the half-life and dosing regimen of each biologic agent.

Aims

To compare neonatal and pregnancy-related outcomes in early versus late dosing of biologics.

Methods

This was a single-center retrospective cohort study conducted at Mount Sinai Hospital from 2016–2021. We included patients with an established diagnosis of IBD before pregnancy who were at least 18 years of age at the time of conception. All patients must have been treated with an IBD-specific biologic agent and had a documented final dose during the pregnancy. The early group received their last biologic dose earlier than the AGA recommendations and the late group received it within the recommended interval. A patient was considered to have a flare based on the overall clinical impression of their gastroenterologist informed by reported symptoms, investigations (fecal calprotectin, endoscopy), and response to treatment. Neonatal and pregnancy-related outcomes were compared amongst the two groups using the student’s t-test (for continuous variables) and Fischer’s exact test (for categorical variables) using SPSS Version 27.

Results

Of 322 patients who had a completed pregnancy at Mount Sinai Hospital, 107 were included in this study. 67 (62.6%) were in the early and 40 (37.4%) were in the late groups. Baseline characteristics including age, comorbidities, IBD phenotype and disease activity were similar between the two groups. The late group had significantly later gestational ages (37.4 vs 38.7 weeks, p=0.006), higher 5-minute Apgar scores (8.7 vs. 9.0, p=0.042), fewer NICU admissions (25.4% vs 5.0%, p=0.036), and fewer IBD flares (28.3% vs 11.1%, p=0.039) in the 6-month post-partum period. There were no significant differences in the rates of premature birth, caesarian sections, infections, and congenital abnormalities. Results are displayed in figure 1.

Conclusions

Our study suggests that late dosing of biologics according to the AGA guidelines was associated with favourable outcomes. However, this is an unadjusted analysis based on retrospective data and findings should be confirmed in a prospective manner to account for confounders.

Funding Agencies

None

A177 INADEQUATE OR EXCESSIVE GESTATIONAL WEIGHT GAIN IN INFLAMMATORY BOWEL DISEASE AND IMPACT ON PREGNANCY AND NEONATAL OUTCOMES

Background

Patients with inflammatory bowel disease (IBD) are at a risk of adverse pregnancy outcomes. Prior studies have suggested that inadequate gestational weight gain is associated with preterm birth and intrauterine growth restriction.

Aims

We sought to characterize the proportion of people with IBD who gain inadequate or excessive weight during pregnancy and how this affects pregnancy and neonatal outcomes.

Methods

Pregnant patients with ulcerative colitis (UC), Crohn’s disease (CD), and inflammatory bowel disease unclassified (IBD-U) were identified retrospectively at Mount Sinai Hospital from 2016 to 2020. Total gestational weight gain (GWG) was calculated as the difference of the weight recorded at time of labor and pre-pregnancy weight. GWG was categorized as inadequate GWG, adequate GWG, and excessive GWG based on the pre-pregnancy body-mass index and standards set by the U.S. Institute of Medicine. Neonatal-related outcomes were also recorded for each patient and included preterm delivery, small for gestational age (SGA) and large for gestational age (LGA). Multiple logistic regression was used to assess the association between gestational weight gain and outcomes while controlling for maternal age, history of gestational diabetes, and preconception disease activity.

Results

225 pregnancies were included (106 UC, 115 CD, 4 IBD-U). Forty-eight patients (21.3%) had inadequate, 91 (40.4%) adequate, and 86 (38.2%) excessive GWG. People of East Asian, African, and Hispanic ethnicity were more likely to have inadequate GWG. People with inadequate GWG were more likely than those with excessive GWG to have lower preconception BMI (21.7 vs 25.5 kg/m2, P=0.001). IBD type was not associated with inadequate GWG or excessive GWG, though people with inadequate GWG were 2-fold less likely to be on anti-TNF therapy. People with excessive GWG were more likely than those with adequate GWG to have babies with higher birth weight (3,364g vs 3,132g, P=0.003). People with inadequate GWG were not at increased risk of SGA compared to those with adequate GWG (adjusted odds ratio (aOR), 1.01; 95% CI: 0.37 – 2.71, P=0.99). Those with excessive GWG were substantially less likely to have an infant with SGA (aOR, 0.23; 95% CI: 0.07 – 0.72, P=0.01). On multivariable logistic regression analysis, excessive GWG was not associated with increased odds of delivering infants with LGA (aOR, 1.46; 95% CI: 0.54 – 3.95, P=0.46). There was no association between non-adequate gestational weight gain and preterm delivery or Caesarean delivery.

Conclusions

Less than half of persons with IBD have adequate GWG during pregnancy. Inadequate GWG was not associated with poor neonatal outcomes, and excessive GWG appeared to protect against delivering infants born SGA.

Funding Agencies

None

A151 COMPARABLE NEONATAL AND PREGNANCY-RELATED OUTCOMES BETWEEN EARLY AND LATE DISCONTINUATION OF BIOLOGICS IN PREGNANT WOMEN WITH INFLAMMATORY BOWEL DISEASE

Background

Inflammatory bowel disease (IBD) disease activity during pregnancy is related to adverse neonatal and pregnancy-related outcomes. Biologics are used to suppress disease activity, however, since there is known transplacental passage, the American Gastroenterology Association (AGA) recommends timing the final dose with drug-specific half-lives although there is little evidence demonstrating adverse outcomes.

Aims

We aim to assess the safety of early versus late discontinuation of biologics according to drug-specific half-lives by comparing various neonatal and pregnancy-related outcomes.

Methods

This is a REB approved single-center retrospective cohort study on all patients with IBD ≥18 years of age on a biologic agent prior to conception, have a documented final dose during pregnancy, and were seen at Mount Sinai Hospital from 2016–2019. Neonate and pregnancy-related outcomes were compared amongst the two groups (Table 1) using the student’s t-test (birthweight, gestational age, Apgar scores) and Fischer’s exact test (NICU admission, congenital anomalies, GBS, chorioamnionitis) analyzed in SPSS Version 27. The level of significance was set at p<0.05.

Results

We identified 53 patients on biologics pre-conception. 26 patients had a documented final dose (19 early cohort, 7 late cohort) and were included in the analysis. Aside from mean birthweight (3014 vs 3561 g, p=0.036), there were no statistically significant differences between the early and late cohorts for gestational age (37.4 vs 39.0 weeks, p=0.20), 1- and 5-min Apgar scores (7.8 vs 8.8, p=0.37 and 8.5 vs 9.0, p=0.49), NICU admissions (p=0.54), congenital anomalies (p=1.00), GBS (p=0.55), and chorioamnionitis (p=1.00).

Conclusions

Overall, our study suggests that early and late discontinuation of biologics have comparable safety profiles based on various neonatal and pregnancy-related outcomes. In fact, we see significantly higher birthweights in the late cohort along with a consistent (non-statistically significant) trend of later gestational ages, and higher Apgar scores. Further, no cases involving NICU admissions, congenital abnormalities, GBS, or chorioamnionitis were seen in the late cohort. Next, we hope to verify our findings by conducting a prospective cohort study with a larger study population and more comprehensive data collection. This will provide higher statistical power and allow for additional subgroup analyses based on objective disease activity (FCP levels) and therapeutic drug monitoring (serum drug levels).

Funding Agencies

None

Three-dimensional viscous Rayleigh-Taylor instability at the cylindrical interface

In this paper, the rotational part of the disturbance flow field caused by viscous Rayleigh-Taylor instability (RTI) at the cylindrical interface is considered, and the most unstable mode is revealed to be three-dimensional for interfaces of small radii R. With an increase in R, the azimuthal wave number of the most unstable mode increases step by step, and the corresponding axial wave number increases as well at each step of the azimuthal wave number. When the amplitude of the wave-number vector is much larger or much smaller than 1/R, the cylindrical RTI is close to the semi-infinite planar viscous RTI limit or the finite-thickness creeping-flow RTI limit, respectively. The effect of the viscosity ratio is double-edged; it may enhance or suppress the cylindrical RTI, depending on R and the amplitude range of the wave-number vector.

Origin of lobe and cleft at the gravity current front

In this Rapid Communication, the Rayleigh-Taylor instability (RTI) along the density interfaces of gravity current fronts is analyzed. Both the location and the spanwise wave number of the most unstable mode determined by the local dispersion relation agree with those of the strongest perturbation obtained from numerical simulations, suggesting that the original formation mechanism of lobes and clefts at the current front is RTI. Furthermore, the predictions of the semi-infinite RTI model, i.e., the original dominating spanwise wave number of the Boussinesq current substantially depends on the Prandtl number and has a 1/3 scaling law with the Grashof number, are confirmed by the three-dimensional numerical simulations.

Unified decomposition method to study Rayleigh-Taylor instability in liquids and solids

In the previous studies of Rayleigh-Taylor instability, different methods were used to consider the effects of elasticity, viscosity, and magnetic fields. In this paper, a unified method, which was first used for fluids, is validated for different physical models, where the unstable mode is decomposed into an irrotational part and a rotational part, and the latter one includes the effects of nonconservative forces and constitutive relations. Previous results of solid and liquid with or without the effects of magnetic fields and finite thickness can be easily recovered after applying the corresponding interface boundary conditions. In addition, new approximate but analytical solutions of the growth rates for a semi-infinite solid-solid interface and solid-fluid interface are obtained with substantially improved accuracy in comparison with the previous ones.

Retarding viscous Rayleigh-Taylor mixing by an optimized additional mode

The Rayleigh-Taylor (RT) mixing induced by random interface disturbances between two incompressible viscous fluids is simulated numerically. The ensemble averaged spike velocity is found to be remarkably retarded when the random interface disturbances are superimposed with an optimized additional mode. The mode's wavenumber is selected to be large enough to avoid enhancing the dominance of long-wavelength modes, but not so large that its saturated spike and bubble velocities are too small to stimulate a growing effective density-gradient layer suppressing the long-wavelength modes. Such an optimized suppressing mode is expected to be found in the RT mixing including other diffusion processes, e.g., concentration diffusion and thermal diffusion.

Nonlinear Rayleigh-Taylor instability of rotating inviscid fluids

It is demonstrated theoretically that the nonlinear stage of the Rayleigh-Taylor instability can be retarded at arbitrary Atwood numbers in a rotating system with the axis of rotation normal to the acceleration of the interface between two uniform inviscid fluids. The Coriolis force provides an effective restoring force on the perturbed interface, and the uniform rotation will always decrease the nonlinear saturation amplitude of the interface at any disturbance wavelength.